Drought Projections Do Not Go Well With Fungicide Applications

Source: Anne Dorrance, Pierce Paul, OSU

Several calls this past week for fungicide applications on corn and soybean at all different growth stages.  So let’s review what might be at stake here.

Soybeans.  Frogeye leaf spot and white mold on susceptible varieties when the environment is favorable for disease easily pay the cost of application plus save yield losses.  Let’s dig a bit deeper.  Both of these diseases are caused by fungi but frogeye leaf spot is a polycyclic disease, meaning that multiple infections occur on new leaves through the season while white mold is monocyclic and the plant is really only susceptible during the flowering stage.  Both of these diseases are also limited geographically in the state.  White mold is favored in North East Ohio and down through the central region where fields are smaller and air flow can be an issue.  Frogeye has been found on highly susceptible varieties south of 70, but it is moving a bit north so it is one that I am watching.

White mold is also favored by closed canopy, cool nights and high relative humidity.  So farmers in these areas should double check their variety ratings first.  If it is moderate to low score for resistance (read the fine print) then this year a spray may be warranted.  We have gotten consistent control of white mold with Endura at R1.  Herbicides that are labeled for white mold suppression have also knocked back this disease, but if a drought occurs or no disease develops, losses of 10% or greater can occur due to the spray alone.  For these purposes R1 is a flower on the bottom of 1/3 of the plants in the field.

Frogeye leaf spot –There also must be some inoculum or low level of disease present in the field for this disease to cause substantial and measurable yield losses.   This disease will only move in the canopy when there is regular rainfall.  And again only on susceptible varieties. With dry weather, this will sit and hold. Time to scout for this will be at the end of flowering if it can be found in the field.  With drought conditions, the disease will not impact the crop.

The story is very similar from a corn pathology standpoint. Most of our major diseases (gray leaf spot, northern corn leaf blight, eye spot) are driven by wet, humid conditions, consequently, the dry weather we have experienced over the last several days will keep most diseases in check. Fungicides are not warranted under these conditions; it just does not pay. Although some product labels may mention yield responses under drought-like condition, our data do not support such a benefit. We see the highest yield responses when fungicides are applied to susceptible hybrids at VT-R1 under disease-favorable conditions. These conditions would include extended periods of dew and high relative humidity, especially during the early- to mid-morning hours.

For a disease like southern rust that usually blows up from the south, and tar spot, an emerging disease of increasing concern in the state, fields should be scouted before making an application. Both diseases develop well under warm conditions, but they also need moisture and high relative humidity to spread. In the case of tar spot, based on what we have seen in 2018 and 2019, it usually develops well into grain fill (R4-R5), and as such, may have little effect on grain yield. Data from some states in the western half of the corn belt show that when tar spot develops early, yield loss may be substantial. The same is true for early southern rust development. So, scout fields to see what is out there and at what level before investing in fungicide application.

Corn and Soybean Seedling Blights

Source: Dr. Anne Dorrance, OSU

Low stands or poor development of plants is, unfortunately, a common occurrence for fields that were planted in many regions of Ohio with heavy soil or are poorly drained soil.  Symptoms include skips, missing plants, or dried up and brown seedlings.  There may also be, wilting plants with and rotten, brown, decaying spots or lesions on the roots. Now is an excellent time to scout stands and check to be sure that the fields are not just crusted over – and that the seeds and seedlings that are there are still healthy.

While there, dig up a few of the affected plants, if the roots are brown and soft, the seedling will die eventually or be very weak.  So don’t count them as part of your total stand.  On soybeans check to see if there are nodules, the corky looking knobs on the roots that help legumes fix nitrogen.  The cold, wet weather does not favor nodulation, so this may take a bit longer, for now, native Rhizobium spp. to get a foothold in the plants.  Once the plants have nodules, they will recover and grow.  On corn, the root (mesocotyl) between the young seedling and the seed, should be white.  If it is dark brown or soft, this will also be a weakened plant.  Some pathogens, if the environment is right, will continue to multiply and grow to kill the seedling.

For management, improving soil drainage, and having at least two ingredients in the seed treatment mixture targeting water molds (Pythium and Phytophthora) are necessary for the challenging areas in Ohio that have a history of replanting.  If you do have to replant, take a look at what the seed treatment package is and note what is in the mix.  The one caution, though, is if the field was submerged for more than 24-48 hours (Ponding), this is flood injury, and there are no seed treatments for this.

Overwintering of Pathogens and Insects – What do Winter Temperatures Tell Us About Next Season?

Source: Anne Dorrance, Kelley Tilmon, Andy Michel, OSU Extension

Over the years we have developed databases of winter temperatures followed by scouting to indicate starting pathogen populations for Ohio.

Frogeye leaf spot – We have documented early infections and overwintering ability of the fungus, Cercospora sojina, that causes frogeye leaf spot. It appears that when there are less than 10 days during the months of December, January and February of less than 17 F, we have had reports of outbreaks of frogeye leaf spot.  This occurred in fields where there was a high level of inoculum at the end of the season the same or similar moderately to highly susceptible cultivar was planted into the same field again which then initiated the epidemic that much sooner.  Losses of greater than 35% in yield or very early fungicide applications were necessary.

Expecting continued warmer winter temperatures, for fields with a history of frogeye leaf spot, and no-till production systems, the first thing for farmers is to do now to mitigate losses in 2020:

  1. Rotate fields with high levels of frogeye leaf spot into corn or another crop.
  2. If it is still targeted for soybean, look at their soybean varieties frogeye leaf spot resistance scores.  Your seed dealer will have more information.  Plan now for what fields they will go into.
  3. Scout the susceptible cultivars much earlier than what we have called for in the past and monitor levels.

Another pathogen that may be more prevalent after a warm winter is Stewart’s bacterial wilt.  This disease is transmitted to corn by corn flea beetle which survives in greater numbers in warm winters. This is a greater problem in popcorn and sweet corn as most field corn has high levels of resistance to the bacterium.

Most other field crop insect pests in Ohio are not highly influenced by winter conditions as they are well-adapted to withstand cold overwintering conditions.  Once exception is Mexican bean beetle, an occasional pest of soybean (especially in central Ohio).  Warm winter conditions may cause higher populations of this insect the following field season.

Tar Spot of Corn in Ohio Again this 2019

Source:  Pierce Paul, Felipe Dalla Lana da Silva, OSU Extension

Tar Spot, a new disease of corn caused by the fungus Phyllachora maydis, was reported for the first time in Ohio at the end of the 2018 growing season. At that time, it was found mostly in counties close to the Indiana border, as the disease continued to spread from the middle of country where it was first confirmed in 2015. Over the last few weeks, there have been several new, confirmed report of Tar Spot in Ohio, this time not only in the northwestern corner of the state, but also from a few fields in central and south-central Ohio. As was the case last year, disease onset was late again this year, with the first reports coming in well after R4. However, some of the regions affected last year had more fields affected this year, with much higher levels of disease severity. It could be that Tar Spot is becoming established in some areas of the state due to the fungus overwintering in crop residue from one growing season to another. This is very consistent with the pattern observed in parts of Indiana and Illinois where the disease was first reported. We will continue to keep our eyes out for Tar Spot, as we learn more about it and develop management strategies. You can help by looking for Tar Spot as you walk fields this fall, and please send us samples.

What does it look like? Even though corn is drying down, if Tar Spot is present, you can still detect it on dry, senescent leaves almost as easily as you can on healthy leaves. So, please check your fields to see if this disease is present. “Symptoms of tar spot first appear as oval to irregular bleached to brown lesions on leaves in which raised, black spore-producing structures call stroma are formed… giving the symptomatic areas of the leaf a rough or bumpy feel to the touch… resembling pustules on leaves with rust. Lesions … may coalesce to cause large areas of blighted leaf tissue. Symptoms may also be present on leaf sheaths and husks.” As the name of the disease suggests, symptoms look like the splatter of “tar” on the leaves. In some cases, each black tar-like spot may be surrounded by a necrotic halo, forming what is referred to as “fish-eye” lesions.

What causes Tar Spot and how damaging is it? In the past, the greatest impact of this disease in terms of yield loss were observed when P. maydis-infected plants were co-infected with a second fungus called Monographella maydis. In other words, the damage tended to be much more severe when the two fungi worked together to affect the plant. So far, only the first fungus, P. maydis, has been reported in the US, but based on work done in Illinois, this pathology alone is capable of causing substantial yield reduction on highly susceptible hybrids when conditions are favorable and infections occur early.  

Where did it come from and will it survive and become established? At this point it is still unclear as to how Tar Spot got to the US in the first place and how it continues to spread. The fungus is not known to be seed-borne or infect other plant species, so corn seeds and weeds are unlikely to be the sources of inoculum. However, the fungus can survive and be moved around on fresh and dry plant materials such as leaves and husks. In addition, since spores of the fungus can be carried be wind, it could be blowing in from neighboring states/counties/fields. Although not yet confirmed through survival studies, it appears that the fungus could be overwintering in infected crop stubble between growing seasons.

What should I do if I find Tar Spot? If you see anything that fits the description of, or resembles (Picture) Tar Spot, please inform your state specialist, field specialist, or county extension educator, but most importantly, please send samples to my lab (1680 Madison Ave, Wooster, OH) for confirmation. We will also be using your samples to study the fungus in order to develop effective management strategies.

Read more about Tar Spot of Corn at:

https://cropprotectionnetwork.org/resources/articles/diseases/tar-spot-of-corn

https://www.extension.purdue.edu/extmedia/BP/BP-90-W.pdf

 

Corn Grain Test Weight

Source: R.L. Nielsen, Purdue Univ. (edited)

Among the top 10 most discussed (and cussed) topics at the Chat ‘n Chew Cafe during corn harvest season is the grain test weight being reported from corn fields in the neighborhood. Test weight is measured in the U.S. in terms of pounds of grain per volumetric “Winchester” bushel. In practice, test weight measurements are based on the weight of grain that fills a quart container (37.24 qts to a bushel) that meets the specifications of the USDA-FGIS (GIPSA) for official inspection (Fig. 1). Certain electronic moisture meters, like the Dickey-John GAC, estimate test weight based on a smaller-volume cup. These test weight estimates are reasonably accurate but are not accepted for official grain trading purposes.

The official minimum allowable test weight in the U.S. for No. 1 yellow corn is 56 lbs/bu and for No. 2 yellow corn is 54 lbs/bu (USDA-GIPSA, 1996). Corn grain in the U.S. is marketed on the basis of a 56-lb “bushel” regardless of test weight. Even though grain moisture is not part of the U.S. standards for corn, grain buyers pay on the basis of “dry” bushels (15 to 15.5% grain moisture content) or discount the market price to account for the drying expenses they expect to incur handling wetter corn grain.

Growers worry about low test weight because local grain buyers often discount their market bids for low test weight grain. In addition, growers are naturally disappointed when they deliver a 1000 bushel (volumetric bushels, that is) semi-load of grain that averages 52-lb test weight because they only get paid for 929 56-lb “market” bushels (52,000 lbs ÷ 56 lbs/bu) PLUS they receive a discounted price for the low test weight grain. On the other hand, high test weight grain makes growers feel good when they deliver a 1000 bushel semi-load of grain that averages 60 lb test weight because they will get paid for 1071 56-lb “market” bushels (60,000 lbs ÷ 56 lbs/bu).

These emotions encourage the belief that high test weight grain (lbs of dry matter per volumetric bushel) is associated with high grain yields (lbs. of dry matter per acre) and vice versa. However, there is little evidence in the research literature that grain test weight is strongly related to grain yield.

Hybrid variability exists for grain test weight, but does not automatically correspond to differences in genetic yield potential. Grain test weight for a given hybrid often varies from field to field or year to year, but does not automatically correspond to the overall yield level of an environment.

Similarly, grain from high yielding fields does not necessarily have higher test weight than that from lower yielding fields. In fact, test weight of grain harvested from severely stressed fields is occasionally higher than that of grain from non-stressed fields, as evidenced in Fig. 2 for 27 corn hybrids grown at 3 locations with widely varying yield levels in Kansas in 2011. Another example from Ohio with 22 hybrids grown in common in the drought year of 2012 and the much better yielding year of 2013 also indicated no relationship between yield level and grain test weight (Fig. 3).

Conventional dogma suggests that low test weight corn grain decreases the processing efficiency and quality of processed end-use products like corn starch (U.S. Grains Council, 2018), although the research literature does not consistently support this belief. Similarly, low test corn grain is often thought to be inferior for animal feed quality, although again the research literature does not support this belief (Rusche, 2012Simpson, 2000Wiechenthal Pas et al., 1998). Whether or not low test weight grain is inferior to higher test weight grain may depend on the cause of the low test weight in the first place.

Common Causes of Low Grain Test Weight

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Considerations for 2019 Wheat Planting

Source: Andy Michel, Laura Lindsey, Pierce Paul, OSU

With the autumn rapidly approaching, wheat planting is likely to begin soon. Planting after the Hessian fly free date remains the best chance to avoid issues with insects and diseases, as well as helping ensure good agronomic quality.  Some benefits of the fly free date:

Hessian Fly: Adults of the Hessian fly lay eggs in emerging wheat. These eggs then hatch into small larvae that feed before spending the winter as a flaxseed. The early autumn feeding will stress the young wheat plant right before the winter, resulting in stunted and wilted plants.  Very little egg laying occurs after the fly free date, which helps to limit infestation. Wheat varieties with resistance against the Hessian are available, in addition to seed treatments, which can help limit damage.

Aphids: Two main aphids infest wheat in Ohio: the English grain aphid and the bird cherry-oat aphid.  These aphids rarely cause economic injury on wheat from feeding. However, they can transmit several viruses that can severely impact wheat including Barley Yellow Dwarf virus.  These aphids do not only feed on wheat, but several other grasses that serve as natural sources of viruses.  If wheat is planted too early, and emerges before the aphids overwinter or stop feeding, they can be early transmitters of viruses.  Although seed treatments could help kill the aphids, they may survive long enough to transmit the virus to the plant.  Any transmission in the autumn would likely serve as a local source in the following spring.

Other foliar diseases: Although not directly related to the Hessian Fly, planting after the fly free date also helps to reduce the early establishment of leaf diseases like Stagonospora leaf blotch and powdery mildew. Planting date is indirectly linked to spore production by fungi that cause these diseases and infection of young plants. The earlier you plant, the more spores are available, and the more suitable (warmer) conditions are for infection. Fall infections often leads to more damage and greater yield loss in the spring, especially of susceptible varieties are planted and not protected with a fungicide at Feeks 8 (flag leaf emergence). As conditions become cooler after the fly free date, pathogens that cause leaf diseases become last active, and as such, are less likely to infect plants.

Delayed Corn Planting the Disease Risk in Corn

Source: Dr. Pierce Paul, OSU Extension

Disease Risk

In Ohio, several foliar diseases are of greater concern in late-planted corn for a number of reasons, including: 1 – for diseases like gray leaf spot (GLS), northern corn leaf blight (NCLB), and eye spot that are caused by pathogens that overwinter in corn stubble, delayed planting allows more time for inoculum (spores) to buildup, especially in no-till, corn-on-corn fields and 2 – for diseases like common and southern rust that are caused by pathogens that do not overwinter in Ohio, planting late allows more time for spore for blow up from southern states. So, with late planting, not only are more spores likely to be available to infect the crop, they are also more likely to infect the crop at an earlier growth stage and under conditions that are more favorable for disease development. Let us use gray leaf spot as an example. In a “normal” year, although lesions may develop early in the season, this disease typically takes off and spreads after pollination (VT/R1) when the number of spores in the air is high and the weather becomes favorable for infection. Depending on where you are in the state, VT/R1 usually occurs sometime in mid-July. Planting late does not prevent spores from building up or conditions from becoming favorable for the gray leaf spot fungus to infect plant in mid-July, however, the primary difference it that instead of infecting plants at the VT/R1 growth state, the fungus will be infecting plants at a much earlier growth stage, V8-V12, for instance. If the hybrid is susceptible and conditions become favorable, high levels of infection at V8-V12 will result in greater and more rapid diseases development, and consequently, greater damage to the upper leaves before grain-fill is complete. This is also true for NCLB, eye spot, and southern rust.

So, what should I do:

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Ponding and Saturated Soils: Results of Recent Ohio Corn Research

Source: Alexander Lindsey, Peter Thomison

Persistent rains during May and early June have resulted in ponding and saturated soils in many Ohio corn fields and led to questions concerning what impact these conditions will have on corn performance.

The extent to which ponding injures corn is determined by several factors including (1) plant stage of development when ponding occurs, (2) duration of ponding and (3) air/soil temperatures. Corn is affected most by flooding at the early stages of growth (see https://agcrops.osu.edu/newsletter/corn-newsletter/2018-15/young-corn-wet-feet-what-can-we-expect). Under certain conditions, saturated soils can result in yield losses. Saturated soil conditions can result in losses of nitrogen through denitrification and leaching. Additionally, root uptake of nutrients may be seriously reduced even if plants are not killed outright by the oxygen deficiency and the carbon dioxide toxicity that result from saturated soil conditions. Root growth and plant respiration slow down while root permeability to water and nutrient uptake decreases. Impaired nutrient uptake may result in deficiencies of nitrogen and other nutrients during the grain filling stage. Once the corn has reached the late vegetative stages, saturated soil conditions will usually not cause significant damage. Moreover, moderate temperatures should help minimize the level of stress.

Although standing water is evident in fields with compacted areas, ponding has usually been of limited duration (i.e. the water has drained off quickly within a few hours). In Ohio in 2017-2018, we observed a 10% yield loss when corn was flooded at V4 for 2 days and received 120 lbs N pre-plant + 60 lbs N sidedress (applied post-flood). When flooded for 4 or 6 days, yield loss increased to 15 and 33%, respectively, when receiving the same N regime. If the additional 60 lbs N was not side-dressed post-flood, yield losses increased to 30, 50, or 57% for 2, 4, or 6 days of flooding, respectively. According to Dr. Emerson Nafziger at the University of Illinois (http://bulletin.ipm.illinois.edu/?p=1240) “…At the time the crop reaches stage V13 (about head-high), it still has to take up 110 to 120 lb of N, and in years when June is wet, a common question is whether or not the crop might run out of nitrogen, leaving the crop short. While the need for 20 or more lb of N per week would seem to raise the possibility of a shortage, the production of plant-available N from soil organic matter through the process of mineralization is also at its maximum rate in mid-season. For a crop with a good root system growing in a soil with 3 percent organic matter, mineralization at mid-season likely provides at least half the N needed by the crop on a daily basis. This means that normal amounts of fertilizer N, even if there has been some loss, should be adequate to supply the crop.”

If the rain has been paired with strong winds, root lodging may occur. Yield losses of 4, 10, and 15-25% have been reported for 100% root lodging at V10, V13-15, and V17-R1, respectively in Wisconsin. Results from Ohio in 2018 suggest these values may be greater than previously reported (8, 37, and 58% yield loss when root-lodged at V10, V13-14, and VT-R1, respectively).  This trial will be repeated in 2019 in Ohio.

Disease problems that become greater risks due to ponding and cool temperatures include Pythium, corn smut, and crazy top. Fungicide seed treatments will help reduce stand loss, but the duration of protection is limited to about two weeks. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage from corn smut and crazy top is difficult until later in the growing season. However, the economic impact of these latter two diseases is usually negligible.

Tar Spot – A “New” Corn Disease

Adopted from: CPN-2012 Corn – Tar Spot, Crop Protection Network

Initial symptoms of tar spot are brownish lesions on the leaves. Black, spore-producing spots appear later, making the leaf feel rough or bumpy. (Purdue Botany and Plant Pathology photo/Kiersten Wise)

Tar spot is a foliar disease of corn that commonly occurs throughout Mexico, Central America, South America, and the Caribbean. The disease was identified in the United States for the first time in 2015 in northern Illinois and Indiana. As of 2018, it has been confirmed in Iowa, Michigan, Wisconsin, Ohio, and Florida.  During the 2018 growing season, the prevalence and severity of the disease increased dramatically, and in some areas tar spot caused substantial yield losses.

In the United States, tar spot of corn is caused by the fungus Phyllachora maydis. The fungus produces small (0.2-0.8 inch), round to semi-circular, raised black structures called stromata.  In severe cases, stromata may also be observed on leaf sheaths and husks.  Tar spot severity on ear leaves at growth stage R5 (dent stage) can exceed 50 percent in susceptible hybrids when conditions are favorable for the disease.

Corn at any developmental stage is susceptible to infec­tion by the tar spot fungus when conditions are favor­able. Disease symptoms have been observed as early as the third-leaf (V3) growth stage in the United States. P. maydis overwinters on infested corn residue on the soil surface, which serves as a source of inoculum for the subsequent growing season. It is not known if P. maydis overwinters on or infects any other plant hosts in the United States.

Conditions that Favor Disease   In Latin America, cool temperatures (60-70°F) and high relative humidity (greater than 75 percent) favor tar spot development. In addition, disease incidence increases when there is at least seven hours of free moisture on the leaves due to rain, fog, or high relative humidity. However, it is not currently known what conditions favor the disease in the United States. In both 2015 and 2018, warm weather and periods of persistent rain and high humidity during the growing season likely favored the development and spread of the disease.

Continuous corn cultivation with minimum tillage practices, and high application rates of nitrogen fertilizer are also positively correlated with increased disease in Latin America. Although corn lines have been identi­fied in Latin America that have resistance to tar spot complex, U.S. observations indicate that most hybrids grown in the North Central region are susceptible to P. maydis (although they differ in susceptibility).

Yield Losses and Impact   Preliminary data from the Midwest indicate that severe tar spot outbreaks can reduce yield by more than 30 bushels per acre. Yield losses are a function of reduced ear weight, poor kernel fill, loose kernels, and vivipary (a condition in which the seed germinates while still on the cob). Observations also suggest that stalk rot and lodging are increased when tar spot severity is high. Severe tar spot also reduces forage quality.

Diagnosis  You can diagnose corn tar spot in the field by examining corn leaves for the presence of black, tar-like spots. To date, tar spot has been observed most often during mid-to late grain fill (growth stages R3-R6) and usually on leaves below or near the ear leaf. You can observe stromata in green and senesced tissues. Occasionally, you may also observe necrotic brown tissue surrounding the black structures, which produces a fisheye appear­ance.

Management  Most of what we know about tar spot has originated from Mexico and Central America. However, differences in the environments, fungal populations, hybrid genetics, and cropping systems may influence disease development in different areas. Our understanding of this disease in the United States is limited because of its very recent history.

However, several management practices may help reduce tar spot development and severity.

  1. Manage residue. Tilling fields buries infected residue and encourages it to decompose, which may help reduce the amount of overwintering tar spot inoculum.
  2. Rotate to other crops. This will allow residue to decompose and reduce the primary It is not yet known how many years it may take to sufficiently reduce inoculum.
  3. Avoid highly susceptible hybrids.
  4. Investigate fungicides. Some fungicides may reduce tar spot, however, we have little data about application timing that will provide an effective and economical response.  Efforts are underway to understand the biology and epidemiology of this disease, which may help formulate fungicide application decisions in the future.

 

What effect will cold temperatures have on pests and pathogens?

Source: the Bulletin, University of Illinois

Many in the Illinois agricultural community are wondering what effects the recent extreme cold might have on pests and pathogens. While it would be nice if the cold temperatures we are experiencing could help to reduce our potential for pest damage, past experience tells us that the most serious pests we deal with are unlikely to be impacted much by these conditions.

Many of the pathogens and insect pests that commonly affect field crops in Illinois are well adapted to survive our winter conditions.  In many cases, pathogens produce recalcitrant survival structures (e.g. cysts in soybean cyst nematode, oospores in Phytophthora, sclerotia in white mold).  These structures allow the pathogen to survive extreme conditions including cold, drought, and flooding. Different species of insects overwinter in different life stages, including eggs (for example, western corn rootworm), larvae (Japanese beetles), pupae (corn earworm, though they do not survive the winter in most of Illinois), or adults (stink bugs). The overwintering stage has characteristics that help these insects to survive the winter, either by adjusting its physiology to better survive the cold, seeking out an overwintering site that protects it (such as soil, tree bark, or leaf litter), or both. The overwintering sites that insects find mean that they are not experiencing the same temperatures that we are when we venture outside. Wind chill has little effect for this reason (even though it has a major, unpleasant effect on us).

Extreme cold temperatures can impact some insects and plant pathogens, particularly those that may not overwinter as well (e.g. powdery mildew).  When cold weather pushes into the Southern regions of the country it can push certain diseases, such as rusts, further south, delaying disease onset in Illinois and other regions further north. The same is true of migratory insects, such as black cutworm and fall armyworm, which do not usually overwinter in Illinois; colder temperatures during winter often delay the arrival of these insects, and may ultimately lead to lower numbers. The opposite is also true – warmer than normal temperatures during the winter can allow these migratory insects to become a problem earlier in the season.

Although cold temperatures may not impact most of the diseases we encounter in Illinois field crops, fluctuation between conditions of cold and warm may have a negative impact on some diseases.  Dormancy by fungican be broken by environmental conditions such as higher temperatures.  This is similar to what occurs in plants, where warm weather may result in trees flushing out buds and flowers.  Consequently, the wide swings in temperature that we have experienced during the 2018/19 winter may negatively impact some diseases. While some insects (such as stink bugs) can also break dormancy during brief warm periods, many of our most serious pests will stay “hunkered down” until the spring and avoid these fluctuations. Unfortunately, insects and plant diseases are unlikely to suffer as much from the recent cold as we have.