Month: June 2019

Cucurbit Powdery Mildew – Start Scouting Now

Powdery mildew arrived this week on squash in Wayne County, Ohio. It is early – usually we see it first in mid-July. The fungus that causes cucurbit powdery mildew does not overwinter in Ohio, so the disease does not appear until spores arrive on wind currents from warmer growing areas. Signs of infection are small circular powdery growths (mycelium and spores of the pathogen) on either side of the leaf. These spots enlarge and can eventually cover most of the leaf surface and kill the leaves. Stems and leaf petioles are also susceptible, but the disease is not observed on fruit. In pumpkins, powdery mildew may also attack the “handles”, which can be further damaged by secondary pathogens.

Powdery mildew is managed using disease-resistant varieties and fungicides. Organic production systems need to rely heavily on resistant varieties but there are OMRI-approved fungicides and biologicals that can reduce disease severity.  These options were summarized in this blog in 2018.  In conventional systems, insensitivity to overused fungicides is common in populations of the fungus that causes this disease, so it is important that a fungicide resistance management program is followed. Remember to alternate fungicides in different FRAC (Fungicide Resistance Action Committee) groups, indicating different modes of action against the fungus. It is important to apply fungicides when the disease first appears and incidence is low. Fungicides that are effective against cucurbit powdery mildew can be found in the Midwest Vegetable Production Guide for Commercial Growers; product ratings and FRAC codes are on page 128. Our evaluations of efficacy of powdery mildew fungicides in Ohio in 2018 indicated that Inspire Super, Procure, Rally, Aprovia Top and Quintec provided very good control of powdery mildew on pumpkins in all three locations (click on graph to enlarge).  In this test, a bioassay, Bravo Weather Stik and Fontelis provided moderate control and Pristine provided poor control. Merivon Xemium and Torino did not perform well in this test (data not included); however efficacy ratings in the Midwest and Southeast vegetable production guides are “good”. Growers should take this into account when choosing products for powdery mildew management.

Persistently-wet Soils Early in the Season: Consequences and Mitigation

The Problem

Too much rain has fallen. Beginning in late autumn 2018, conditions turned wet and have persisted throughout the winter and spring seasons of 2019. For example, the OARDC-Wooster weather station (https://www.oardc.ohio-state.edu/weather1/) registered rainfall on 47 days of the 88-day period April 1 – June 27, totaling 13.4 inches over the period (an average of nearly one-third inch of rainfall per day with rain). Not surprisingly, impacts have been accumulating. Much has been lost directly due to rain and rain-related delays: time, topsoil, fertilizer, targeted levels of stand establishment, and opportunities to start well with weed, pest, and disease management, and other operations. These primary consequences have had secondary ones. Field preparation and stand establishment is always a hectic phase and outcomes are never certain, even in years when weather is largely a neutral factor. Still, routines and schedules can follow a familiar timeline. Not so for many in 2019. Timelines and various common expectations have gone out the window (or, into the drainage ditch, as it were) and management has been more “seat of the pants” than many prefer. We’ve been required to reconsider what to do, when, how, etc.

A Set of Partial Solutions

Conditions can improve with a little cooperation from the weather and strategic action. What follows is a brief overview of factors to consider and steps to take when given a chance: (a) to kick-start or rejuvenate a stand or crop set back by persistently wet or saturated soil since seeding or transplanting or (b) to limit the recurrence of the same problem in future seasons. The amount of detail available for each factor and step could fill at least several VegNet articles. This article is more broad than deep and it draws from experience and excellent references developed through the years by members of the industry and vegetable research-extension community.

For 2019

1. Surface cultivation. Persistent or pounding rain can lead soil to crust. Crusting prevents seedlings from emerging, air from entering the soil, and some wastes in the soil from leaving it. Breaking the crust with light surface cultivation can help reverse these conditions. Choose the right time and equipment for the operation in order to maximize its benefit while minimizing the potential for creating compaction while heavy equipment is taken across the field with subsurface soil moisture levels still relatively high.

2. Careful cultivation and irrigation. Many now face a situation in which leggy, under-nourished, and generally weak transplants were set into soils wetter than ideal and which remained wet for long stretches thereafter. Not good. Root-shoot ratios are not ideal and root systems may be small and shallow, concentrated near the soil surface. This makes root systems prone to damage due to cultivation and ironically, plants susceptible to LOW moisture stress, especially if weather turns dry AND warm. Keep alert when cultivating, maintain the proper depth and distance from the crop. Also, as we shift toward a more summer-like pattern of scattered but intense rainfall, treat it as an opportunity to encourage root systems to expand and deepen. Doing so may require “weaning” plants off the saturated conditions many have experienced since planting. Guard against strict adherence to irrigation schedules based on a “normal” year with normal stand establishment conditions. Modify how often you irrigate and for how long the water flows each time according to soil and plant conditions, monitoring both carefully. Again, shallow- and small-rooted plants need time to adjust to drier conditions and the process largely cannot be rushed. Consider lengthening the time between irrigations gradually until you are confident the crop has, more or less, fully recovered and “toughened up” and you have reached an adequate level of control over soil moisture and other conditions.

3. Replant. Recall that the growth and productivity of individual plants can hinge on how many neighbors it has and where they are located, i.e., the plant population or density. Compensation allows some crops to produce similar yields across a wide range of plant populations. For these crops, thin stands can be less problematic because yield potential is maintained. However, for non-compensators (e.g., fresh market sweet corn), one less plant clearly results in less yield (e.g., one less ear to sell). Replanting may be more beneficial with crops that do not compensate. Regardless, check records, estimates of days to maturity, etc when selecting varieties and choosing to replant. Also, when replanting flooded-out portions of large plantings, be aware that the crop maturity in these replanted, “pieced in” areas will be different than the main crop but may maintain income potential that would be lost otherwise. These areas may also require slightly different management (e.g., fertilizer, irrigation, protection) than nearby areas planted earlier.

4. Replace. IF and only IF circumstances call for it and allow, replace the vegetable planting with a cover crop, forage/feed crop, or clean fallow program. This step has huge implications for the business and others for the soil. If the very weak or absent vegetable planting can be replaced by clean fallowing or a crop involving less expense, time, and effort but offering some soil building and/or cash-flow potential, this option may represent taking two steps forward starting from one back, i.e., a net gain compared to replanting or continuing with a very weak vegetable crop.

5. Keep planting. Vegetable and grain farmers have been hit hard by the weather so far. One aspect of vegetable farming that can help farmers through these difficult times is that many vegetable crops can be harvest-ready in much less time than full-season corn, soy, and other crops. Enough season remains to plant and harvest a profitable vegetable crop. Talk with your produce buyers. Discuss the possibility of adjusting marketing/delivery scenarios and schedules with, for example, late plantings of early-maturing crops such as sweet corn, green beans, peas, transplanted cole crops, radishes, turnips, daikon radish, zucchini and yellow squash, cucumbers and pickles. Recall that most concentrated-set pickle varieties can be harvested 60 days from planting and northwest Ohio farms traditionally plant through early July.

6. Fertilizer application. Excess rain during stand establishment like many have experienced limits root growth and can allow fertilizer applied before or at planting to leach, runoff, or change form and become unavailable or taken-up less efficiently. Therefore, nutrient deficiencies, especially of nitrogen and potassium, may develop soon after growing conditions improve. Research and experience have shown that applying carefully determined, low amounts of N and K through fertigation, or as a sidedress, broadcast, or foliar treatment, can limit the progression of yield reductions caused by excessive soil moisture. Use plant tissue testing and petiole sap analysis to monitor plant nutrient levels useful in determining if fertilizer applications are needed. Review https://edis.ifas.ufl.edu/pdffiles/EP/EP08100.pdf and similar resources for additional information.

7. Support. Anchoring the plant is one of the six major functions of root systems. Anchoring is difficult in saturated soils and/or when root systems are small, especially compared to the canopy. Don’t underestimate the value of a trellis in supporting upright fruiting crops (e.g., tomato, pepper). It lowers the risk of lodging and wind-whipping (wind-whipping is more likely when transplants were particularly leggy).

For Future Seasons

8. Lengthen rotations and build soil internal drainage and moisture holding capacity. All the familiar approaches – e.g., cover cropping, soil amendments, tiling – apply here. Reduced-tillage approaches are less familiar to some but gaining attention.

Clean fields planted on the flat or then formed into raised beds topped with drip tape and plastic mulch are the current standard among commercial growers throughout much of the world. These standard systems have been very reliable and productive. Reduced-tillage systems, on the other hand, offer various benefits although, historically, their yields are often lower than yields in standard systems. Research by farmers and others has focused on retaining the benefits of reduced-tillage approaches while increasing the yield of systems involving them. For example, at OARDC, we have been investigating whether the use of grafted plants and/or microbe-containing crop biostimulants can enhance yield of tomato grown in a flat-ground, strip-till system. Results have been promising; using one or both treatments has narrowed the gap between yields of the strip-till and standard systems. Regardless, our experience and data collected by others also suggest that soils in strip-till plantings can be more resistant to flooding and resilient when flooding conditions develop.

9. A genetic solution to flooding. Flooding is a problem worldwide in agriculture and plant breeders have taken note. Flooding tolerant rootstocks are available for tomato and ones may become available for other crops that are routinely grafted (pepper, watermelon, cucumber, cantaloupe). Pay attention to flooding tolerance and other grafting-related developments.

10. Study up. It will also remain important to pay close attention to information provided by the climate services community, which includes agroclimatology and other experts. Descriptions of historical trends and projections of future scenarios are constantly improving. My non-expert reading of some recent reports (e.g., see June 8 VegNet) suggests that conditions so far in 2019 are consistent with projections outlined in those reports – e.g., intense rainfall events occurring more often and becoming stronger, allowing for fewer days to complete field work. No one knows for certain that conditions many have encountered so far this season will repeat (weather variability). Still, for planning purposes, a broad reading of various reports can lead one to conclude that conditions so far in 2019 are better viewed as an extreme version of an emerging trend, not a fluke or once in a career scenario.

Brad Bergefurd of OSUE and Jason Cervenec, Education and Outreach Director of the Byrd Polar and Climate Research Center (BPCRC) and Aaron Wilson, Research Scientist with OSU Extension and BPCRC, both with the State Climate Office of Ohio (https://climate.osu.edu/), contributed to this article.

Keeping Tomatoes Healthy in Wet Weather

We are in the middle of a period of wet weather that is predicted to deliver multiple inches of rain to central Ohio and even more to other soaked parts of our state.  Tomatoes are a crop that can suffer several problems related to heavy rainfall that can shorten the harvest period and affect yield.  There are a few things that the backyard grower, community gardener and urban farmer can do to keep their tomato plants healthy and productive though heavy rain periods.

Key Garden Tasks to Keep Tomatoes Healthy in Wet Weather

  • Mulch – organic or non-organic can both be used.  Be careful if your plasticulture is not permeable to air and water,  the heavy constant rainfall may saturate the soil and drown the roots if the soil cannot dry out. Mulch also acts as a barrier to keep soil borne fungal spores off lower tomato leaves.
  • Fertility – contstant rainfall can leach fertility from soil making it unavailable to the plants. Make sure to monitor plant growth and health carefully to avoid a nutrient deficiency.  Foliar feeding can be used when the ground is too saturated to irrigate with water soluble fertilizer.
  • Pruning – promote air circulation by pruning lower leaves.  Try to minimize lower leaf contact with soil.  Use sterilized pruners to remove any diseased leaves and make sure to put diseased leaves in the garbage and not the compost after pruning.

 

This plant needs mulched around the base to prevent soil borne fungal spore contact with leaves. Pruning of the lower leaves will also promote air circulation to assist in disease prevention.

 

These discolored leaves suggest fungal disease in this tomato plant. The leaves need pruned with sterilized pruners and then discarded into the garbage and not the compost pile.

 

This tomato has both organic and plasticulture mulch at the base to keep fungal spores in the soil and off plant leaves. Pruning needs to be done to allow air circulation at the base of the plant.

 

This tomato plant has had lower leaves removed for air circulation with a combination of compost and plasticulture mulch at the base of the plant.

 

Monitor tomatoes carefully for signs of blight, remove the diseased leaves promptly with sterilized pruners and dispose of disease materials in the garbage, not the compost pile.

Make sure to address fertility needs as production increases.  Heavy rain can leach nutrients into the subsoil where they are unavailable to plants, decreasing yield as the season progresses.

Ohio State University Extension has an excellent fact sheet on Growing Tomatoes in the Home Garden.   There is also a plant disease diagnostic laboratory on campus where the grower can send samples if an accurate diagnosis needs confirmed on possible diseased leaves.

Introduction to Using Mustard Cover Crops for Biofumigation in Pumpkin

This article is an introduction to the general processes and basic steps of how to use mustard cover crops to reduce soil borne diseases, such as Plectosporium, in pumpkin. Research using mustard plants to naturally biofumigate soil to allow for more normal yield and fruit quality, has been conducted in several states and Canada, sometimes with mixed results. The results of this trial will be released in a report later in the season.

Mustard cover crop in full bloom.

The field intentionally selected for this trial was cropped to pumpkin in 2018 and exhibited high amounts of Plectorsporium infections on both plant and fruit. The general recommendation for a field infested with this disease would be to rotate away from cucurbits for 3-5 years. Instead of rotation, we are investigating the use of biofumigation as a means to reduce disease incidence.

In mid-April when conditions were suitable for direct seeding, Pacific Gold (6lb/A), Caliente 199 (10lb/A), and a 50/50 blend of the two were drilled into plots at the Western Ag Research Station in South Charleston. Prior to seeding, 100 lb/A of urea and 34 lb/A ammonium sulfate were broadcast and incorporated to increase the biomass and glucosinolate levels of the cover crop. Glucosinolates are the compounds responsible for the biofumigation effect and are released when the mustard plant tissue is macerated and incorporated into the soil. The production of these compounds peak during flowering.

Once peak bloom has been reached it is necessary to mow the plants, immediately followed by incorporation (such as rototilling), packing, and then sealing the soil with water. Once these steps have been performed, the glucosinolates are broken down into other compounds in the soil such as isothiocyanates, where they begin the biofumigation reactions. It is recommended to wait 7-10 days after incorporation to either direct seed or transplant. We seek to confirm the necessity of the waiting period by both seeding and transplanting pumpkins one day after incorporation; we’ll report if any negative effects are seen on the germination rate or growth of the transplants.

To hear more details about the trial and see all steps including the incorporation of mustard cover crop, watch this video posted to the OSU IPM YouTube channel: https://youtu.be/Taz-PhDphhA

If you have worked with mustard cover crops before and have any experiences positive or negative to share, please send them to me at jasinski.4@osu.edu.

Make a Withdrawal from your Soil Weed Seed Bank: Stale Seedbank Technique

Ah spring!  The war against weeds begins anew. The first major skirmish of the growing season should happen before planting. The stale seed bed technique is an often over-looked practice that can be used before planting. It works by first encouraging weeds to sprout and then killing them when they are young and most vulnerable. For organic growers, a stale seed bed can replace the effects of a pre-emergence herbicide. And when used properly, it can contribute to both short-term and long-term weed management.

Weed control can be handled with short-term or long-term approaches. Short-term management focuses on controlling weeds during the first part of crop growth when weeds are more likely to affect crop yields. Long-term weed management, however, works all season-long to deplete weed seeds from the seedbank (the reservoir of viable weed seeds in the soil). Whichever approach you take, using a stale seed bed is a great cultural weed control technique.

To use the stale seed bed most effectively, start several weeks before planting. An initial cultivation kills any emerged weeds that have overwintered. It also brings weed seeds to the surface where exposure to light and oxygen stimulate germination. Depending on the weather and types of seeds present in the soil, weeds may sprout up overnight or over a few weeks. When weeds have germinated and are still small and young, they are easy to kill with a second light cultivation. This process is then repeated as needed and as time allows. As few as three cycles of light/ shallow tillage can reduce the number of subsequent weeds noticeably. For fields and gardens with very heavy weed infestations more cycles of repeated tillage over a few years will be needed. Using a stale seed bed may push back your planting date; but in the absence of weed competition, the crop will have more access to water and sunlight and be able to make up for lost time.

Keys to Success

  • Do not allow emerged seedlings to grow large. It is best to till lightly just as the first seedlings are emerging as this and the earlier ‘white thread’ stage are the most susceptible to desiccation. The more time new weeds have to develop roots, the harder they become to kill with a shallow cultivation.
  • Keep the cultivation shallow to avoid bringing new weed seeds to the surface. The implement used to stir the soil should not go deeper than 2 inches with most of the stirring in the top inch.
  • The technique is dependent upon having adequate soil moisture. Under drought conditions preparation of a stale seedbed may require irrigation to stimulate weed seed germination.
  • Deeper initial tillage can be used to bury an existing weed problem. Tillage, especially when done with a disc or a power tiller, distributes the previous year’s weed seeds throughout the top 6 inches or so of soil. In contrast, an inversion tillage that turns sod upside down will place last year’s seeds 6 inches or so under the surface. From there they are unlikely to emerge unless further discing or lighter tillage moves them closer to the surface. Used skillfully, a deep inversion plowing followed by stale seed bed can put a serious surface weed problem out-of-sight and out-of-mind, at least until the next time the field is plowed deeply.

Stale Seedbed is most effective when it is part of a zero weed threshold system.

The common short-term approach to managing weeds, (weed scientists usually call this the “critical period approach”) is to control weeds aggressively during the first 4-6 weeks after the crop is planted. This 4-6-week period is the critical period during which crops stands are established and yield is secured. Afterwards weeds are of less threat to production; therefore, many farmers scale back control efforts. However, weeds that grow before and after the critical period are still a problem. If allowed to flower and set seed, they will be planting a future crop of weed problems. A long-term approach to weed management, called zero weed seed threshold, requires constant diligence and removal of all weeds before they produce seeds–even after harvest. Research indicates that 3-4 years of using this approach will result in a field with relatively few weeds, provided weed seeds are not introduced from without the field (in seed, irrigation water, on equipment, etc.).

Both short-term and long-term approaches have benefits and drawbacks, many of which depend on a farmer’s individual goals, crops, and available resources. A new online tool from Ohio State allows farmers to think through various weed control approaches in the context of their own individual situations. For those looking to make changes to their weed management, the Organic Weed Decision Making Tool, shows pros and cons of various strategies over time and gives steps to implementing new tactics. Learn more at go.osu.edu/eco-weed-mngt.

More and Better Tools to Help Respond Effectively to Weather-related Challenges

A vegetable farmer pointed out to me recently that “rain” is a four-letter word and that like other ones, he likes rain to fall in just the right amount and at just the right time. Well, although we can’t control when, where, or how much rain will fall, many people in agriculture and the area known as climate services are working to develop reliable forecasts of and effective responses to current and future weather.

Shared commitments to that goal were evident throughout the recent Climate Services Summit (https://climate.osu.edu/news/byrd-center-hosts-ohio-climate-services-summit) coordinated by the State Climate Office of Ohio based at The OSU (https://climate.osu.edu/). Just as important, steps to providing farmers and others with better decision-aids also became clearer through discussions at the program. Ohio State University Extension contributes to the process – for example, see resources, programs, and input offered by Aaron Wilson, Jason Cervenec, and John Fulton – and addressing weather-related challenges and needs of vegetable growers will be important going forward. These were summarized well in two recent reports (https://www.climatehubs.oce.usda.gov/archive/sites/default/files/Midwest_Climate_And_Specialty_Crops_2015_508.pdf and https://store.extension.iastate.edu/product/15448) but more input is always welcome.

Throughout much of this field planting season, many have needed to scramble, improvise, and work round the clock to get work done as weather, soil, labor, and other conditions allowed. It seems that most have experienced the dark side of their share of passing fronts, with few farms experiencing clear skies and calm winds for extended periods. Overall, this seems consistent with information in http://glisa.umich.edu/media/files/GLISA%202%20Pager%202019.pdf (GLISA also participated in the recent Summit). Field and high tunnel plantings have been affected in their own ways by recent conditions, although it is fair to say that most high tunnel plantings were able to remain on schedule, an important early step toward a successful season. Ideally, we will soon see that high tunnels are just one of many key tools available to help maintain and enhance vegetable production amidst changing and increasingly extreme conditions.

Spotted-wing Drosophila are slowly becoming active

Since 2012, Extension educators and a handful of state specialist have set out traps to monitor when spotted-wing Drosophila (SWD) begin to migrate from their overwintering locations into cultivated small fruit fields where growers have to actively manage them. This year, only two counties, Franklin and Greene, have traps out early to monitor for this pest ahead of the dozen or so county network sites that will become active in mid-June.  Franklin county has caught 26 SWD in 2019 but only back in January, nothing more recent. The Greene county site caught two SWD last week (May 28), one in a wood line and one at the edge of a blueberry field but none this week. Recall that the threshold is one fly to begin management when the fruit begins to ripen or is ripe. So, the message is the adults are slowly becoming active, and as the weather warms and fruit begins to ripen, be on the lookout for SWD.

For tips on how to identify, monitor, and manage SWD, check out OSU’s resources at http://u.osu.edu/pestmanagement/pests/swd/and the SWD section of OSU’s IPM YouTube channel https://www.youtube.com/channel/UCzcWaLH3mx7HUKh4OF7bYPA