Late Season Insect Pests of Pumpkin – Jim Jasinski & Celeste Welty

Growers have another 5-6 weeks to protect their pumpkin crop from insect pests such as squash bugs, spotted and striped cucumber beetles, and possibly aphids.  Read the guidelines below for tips on how to manage these late season pests.

Squash bugs – These brown adults and gray nymphs are true bugs that have been slowly building in number through the summer and now seem to be everywhere in the field. They have sucking mouth parts, and feed by piercing the stems, petioles, leaves and fruit trying to get a meal. The time is past for spreading any diseases but in large numbers they can damage fruit and collapse foliage. Thresholds to control these bugs vary by stage but generally more than 1 egg mass per plant or more than 1 adult per plant can be used. Nymphs are generally easier to kill than adults but treatment is only recommended if squash bugs exceed the threshold. See insecticide options at the end of the article.

Adult and nymph squash bugs on handles, fruit, and foliage.

 

 

 

 

 

 

 

 

 

Striped and Spotted Cucumber beetles – These black and yellow striped or spotted beetles have been quietly residing in pumpkin and squash flowers for most of the season, but now that the fruit is maturing, fewer flowers if any are being produced. Beetles are now moving from the flowers back into the canopy and onto the fruit, where they can feed on the rind and the handles, causing significant cosmetic damage. To protect the quality of the fruit and handles, foliar insecticide applications should be made only if beetles are seen actively feeding and scarring the rind.  See insecticide options at the end of the article.

Spotted cucumber beetle.

Striped cucumber beetle.

Cucumber beetle feeding damage on rind.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Aphids – These small soft bodied sucking pests usually move into fields in mid to late August, and can be found on the lower leaf surface. As a consequence of treating for cucumber beetles and squash bugs, a rapid increase in aphids may be seen when foliar insecticides are used, as most broad spectrum insecticides knock out natural enemies of aphids such as ladybeetles, parasitoid wasps, green lacewings, etc. When large aphid populations inhabit a field, production of honey dew and subsequent blackish sooty mold can be found on the pumpkins. The sooty mold can be wiped off and does not damage the fruit.

Sooty mold on pumpkin fruit.

 

 

 

 

 

 

 

 

Products used to control squash bugs, cucumber beetles, and aphids can be found in the Midwest Vegetable Production Guide chapter on Pumpkin (https://ag.purdue.edu/btny/midwest-vegetable-guide/Documents/2017/104_Cucurbits.pdf).

Getting to the Root of the Matter: Soilborne Diseases of Tomato

It is often easy to tell if a plant is sick when it is covered in spots or leaves and fruits are rotting away, but it can be much more difficult to tell when a plant has an infection in its roots or stems. These lower portions of the plant are essential for health and productivity, but are often attacked by pathogens that reside in the soil. Below are some of the most important soilborne diseases of tomatoes and methods for managing them.

How to identify soilborne diseases of tomato

V-shaped necrosis and yellowing of leaves characteristic of Verticillium wilt.

In general, some clues that indicate if a tomato has a soilborne disease includes stunting, wilting, yellowing, dieback and reduced yield. These are also symptoms of nutrient deficiencies and some viruses, so it is important to rule out these possibilities.

Verticillium wilt: Distinctive V-shaped lesions form on the edges of leaves, with V-shaped dead tissue surrounded by a yellow halo. Plants wilt and have yellowing and dieback. Plants may wilt during the day and recover overnight. The inside of the stem has brown discoloration.

Tomato plant with Fusarium wilt. Note the yellow discoloration on only half of the plant.

Fusarium wilt: Plants have yellowing, dieback, and wilting. Sometimes only half a leaf or leaves on only one half of the plant turn yellow and die. The inside of the stem has brown discoloration near the soil line and discoloration may continue up the stem. Roots may look brown and rotten.

Corky root rot: Plants may appear slightly yellow and have weakened growth. Roots appear to be dry, brown, and cracked and have a similar appearance to tree bark. Cracked areas usually occur in distinctive bands and may be swollen. Dark brown cracking may occur on the crown and taproot of the plant.

Black dot root rot: Roots are discolored, usually a honey-brown to grayish-brown, and are speckled with black dots.

Root knot: Roots are misshapen with small to large nematode-induced galls. Galls may range in size from pin-head to finger-sized. Golden-brown dots (egg masses) may appear on the outside of galls. Plants may appear stunted and weak.

Roots with severe corky root rot. Note the cracked, corky, bark-like roots.

Roots with sclerotia of Colletotrichum coccodes, the causal agent of black dot root rot. The honey brown discoloration is also characteristic of this disease.

 

Tomato roots with severe root knot nematode galling.

What causes these diseases?

Verticillium wilt is caused by the fungus Verticillium dahliae, which has an extremely broad host range. There are two races of V. dahliae that infect tomatoes.

Fusarium wilt is caused by the fungus Fusarium oxysporum f. sp. lycopersici and there are three races that infect tomatoes. The pathogen is an excellent soil survivor.

Corky root rot is caused by the fungus Pyrenochaeta lycopersici and survives in soil via microsclerotia that form on roots.

Black dot root rot is caused by the fungus Colletotrichum coccodes, which also causes anthracnose on tomato fruits. The pathogen is capable of surviving in soil by microsclerotia that form on infected fruit and roots (the black dots).

Root knot nematodes belong to the genus Meloidogyne. Both the northern root knot nematode (Meloidogyne hapla) and southern root knot nematode (Meloidogyne incognita) are present in Ohio tomatoes. In general, M. hapla forms smaller, distinct galls on tomato roots, while M. incognita tends to form larger, fused and malformed galls. Both species of nematodes have extremely broad host ranges.

How can I manage these diseases?

When managing soilborne diseases, growers should combine management practices that prevent existing soilborne pathogen populations from increasing with practices that actively reduce pathogen populations in the soil.

  1. Prevention: For transplant production, always use clean planting materials including seed, soilless media (recommended) and well or “city” water for irrigation. Ensure that seedlings are healthy before transplanting. Maintain proper fertility and watering to ensure healthy seedling development and maintain adequate nutrient and water levels throughout crop development.
  2. Sanitation: Remove diseased plants and diseased plant parts. Clean soil from boots and equipment between fields and high tunnels. Do not move from soilborne disease-affected fields to non-affected fields.
  3. Rotation: Rotate out of the same plant family when possible. For pathogens with extremely wide host ranges, such as Verticillium sp. and Meloidogyne spp., it is difficult to rotate to a suitable non-host crop. Since most soilborne pathogens are excellent soil survivors, rotations of 3-5 years are usually necessary to reduce pathogen populations adequately.
  4. Host resistance and grafting: Resistant varieties should be selected whenever possible and resistance to Verticillium wilt and Fusarium wilt is incorporated into most modern tomato varieties. Grafting a disease susceptible scion onto a disease resistant rootstock can reduce damage due to soilborne diseases. Many commonly used rootstocks have resistance to Verticillium wilt, Fusarium wilt, corky root rot, and some resistance to root knot nematode.
  5. Soil disinfestation: Several soil disinfestation options are available that vary in cost, efficacy, and environmental impact. Chemical fumigation and steam sterilization are two options that have been used historically, but are often not feasible for use on vegetable farms. Anaerobic soil disinfestation is a newer method of soil disinfestation that involves amending, saturating, and tarping soil. Soil solarization uses solar-generated heat trapped under plastic sheeting to kill soilborne pathogens, but this technique is not often effective under Midwestern conditions. Soils can be flooded or left fallow to kill pathogens over a period of time, but these methods are often ineffective due to the survival structures of most soilborne pathogens.
  6. Chemical or biological control: Few options are available and many biological control options are still experimental.

Article contributed by Anna Testen and Sally Miller, The Ohio State University Department of Plant Pathology

 

Downy Mildew Confirmed in Pumpkin and Zucchini in Ohio

Zucchini leaf with severe downy mildew. Small blocky lesions are yellow initially, then turn brown as leaf tissue dies. Diseased areas merge and eventually entire leaves die.

While we suspected that downy mildew might be present in southern or central Ohio based on weather conditions, storm trajectories and outbreaks in other states, we had not confirmed it until this weekend in pumpkins and today from zucchinis. The Pike County pumpkins were in a cultivar evaluation trial at the OSU-OARDC South Centers near Piketon. The zucchinis came from two organic farms in Guernsey County. The organic growers indicated that they had observed downy mildew symptoms about 2 weeks ago.

None of the fields had been treated with fungicides effective against downy mildew. As you can see in the zucchini leaf photos in this post, downy mildew can be very severe on squash; similar symptoms can occur on pumpkins. Fungicides should be applied before symptoms are observed – recommended fungicides can be found here.

Organic growers have limited options for downy mildew management. OMRI-approved copper-based fungicides are somewhat effective if applied preventatively. In the chart below, you can see that control varies by year –  in this case good in 2014 and poor in 2013. In both years, downy mildew was significantly less severe in cucumbers treated with Champ WG, oxidate or neem oil  than in non-treated control cucumber plants. Since these are all protectant fungicides, it is critical that they be applied before plants are infected with the downy mildew pathogen. In a separate study conducted at the University of Maryland (Everts & Newark, Plant Disease Management Reports 8:V210), Champ WG alternated with Serenade Soil or Actinovate was as effective as Champ WG alone in reducing downy mildew severity in both cucumber and muskmelon.

Click on chart to enlarge.

Are Pumpkin and Squash at Risk for Downy Mildew in Ohio?

Severe downy mildew on pumpkin, 2015.

Downy mildew has still not been confirmed on pumpkins and squash in Ohio, although the disease is widespread on cucumbers and melons throughout most of the state. This is the time of year when we really start to look for downy mildew on squash and pumpkins, as strains of the pathogen that attack these crops move into the area from the south, usually aided by remnants of hurricanes or tropical storms that reach Ohio. Remnants of tropical storm Harvey are likely to reach southern Ohio at least by Friday. Downy mildew spores can be transmitted long distances in the air, and are brought to the surface by rain.  We are particularly concerned with outbreaks reported in Kentucky on butternut squash this week (http://cdm.ipmpipe.org/scripts/map.php), an indication that the pathogen is established in the area and can serve as a source of inoculum for areas to the north and east.  Growers in southern Ohio should be especially vigilant, although we recommend stepped-up scouting of pumpkins and squash, and application of protectant fungicides, throughout the state.  Fungicide recommendations can be found in my June 28 post.

Corn earworm present at high density

As reported in VegNet last week, the corn earworm population is on the increase in Ohio. At our research farm in Columbus, there were 60 corn earworm moths caught in our pheromone trap during the previous week (13-19 August), and this increased to 577 moths caught in the week that is now ending (20-26 August). Sixty moths in one week is considered to be moderate pest pressure, while 500 moths in one week is considered to be very high pest pressure. Sweet corn that is in the silking stage is at risk of infestation by corn earworm larvae unless it is sprayed with insecticide every 3 days. Details about spray intervals based on trapping can be found at: http://u.osu.edu/pestmanagement/files/2014/12/CornTrapInstructions2009-u47rp3.pdf . Beware that when earworm moths are abundant, control by pyrethroid insecticides (Warrior, Mustang Maxx, Baythroid, Asana, Permethrin, Brigade) has tended to be fair to poor during the past few years due to the development of resistance. Alternative insecticides are Coragen, Radiant, Blackhawk, and Lannate. Entrust is a good option for organic production.

Sweet corn that is genetically engineered to produce the B.t. toxin, as in the Attribute and Attribute II hybrids from Syngenta, and the Performance hybrids from Seminis, offer some protection from infestation by earworm and other caterpillars. These B.t. hybrids were excellent for caterpillar control when first introduced, but in the past few years, hybrids in the Attribute and Performance series are showing only moderate protection from earworm if not supplemented by insecticide sprays, whereas the Attribute II hybrids are still showing excellent control of earworm and other species. A supplemental insecticide spray can be applied when 75-100% of plants have fresh silk, which is a few days later than the typical first spray on non-BT corn.

Weekly catch of corn earworm at several sites is shown on our online Ohio trap report page: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit?usp=sharing , where there is a tab for this species and several other pests along the bottom of the sheet.

 

Cucurbit Downy Mildew Update – Two More Ohio Counties

Map of downy mildew reports in Ohio (all on cucumber or melon) and neighboring states, August 21, 2017. Red indicates reports within last 7 days. www.cdmipmpipe.org

Downy mildew was confirmed on cucumbers in two additional Ohio counties late last week: Harrison and Licking. We still have not confirmed downy mildew on pumpkins or squash in any part of Ohio.  On today’s Cucurbit Downy Mildew ipmPIPE conference call,  none of the representatives from nearby states (MI, WV, VA) reported seeing downy mildew on pumpkins or squash yet this season. However, downy mildew has been reported recently  on jack-o-lantern pumpkins in two counties in northwestern Indiana.  Careful scouting of pumpkin and squash fields should remain a priority.

Downy mildew can be confused with powdery mildew at very early stages of the latter (before the white powdery colonies appear), especially if the pale yellow areas on the top of the leaves are very dense.  Symptoms of other diseases including angular leaf spot and bacterial spot can also be confused with those of downy mildew.  If in doubt, please send a sample to your county educator or directly to the OSU Vegetable Pathology Lab in Wooster, OSU-OARDC, 1680 Madison Ave., Wooster, OH 44691; ph. 330-263-3838.

We are in the process of evaluating commercially available fungicides for efficacy against downy mildew using a bioassay. We will have results within a few weeks. However, we are not aware of new fungicide failures in other parts of the US this season, so our fungicide recommendations posted on June 28, 2017 remain in place.

Corn earworm alert

Every year in August, we are on the lookout for the arrival of large numbers of corn earworm moths that migrate into Ohio from the southern USA. Over the past three days, we have seen a surge in the catch of corn earworm moths in our pheromone trap in Columbus; the catch from Monday (8/14) to Wednesday (8/16) was 11 moths, but the catch from Wednesday (8/16) to Friday (8/18) was 41 moths, with a total of 60 for the full week. We have corn earworm pheromone traps at eight other locations in Ohio; last week these were reporting a catch of only 0 to 3 moths in one week, but it is likely that the catch at these other locations will show an increase during the coming week. Now that most of Ohio’s grain corn is starting to dry out, any patches of sweet corn will be more likely to be attacked by this pest. Once corn earworm is detected, silking sweet corn should be sprayed with insecticide every 2-6 days to prevent injury to kernels. The choice of an appropriate spray interval is as important as the choice of product to use. Details about the most appropriate spray interval based on pheromone traps are shown in the chart below.

Although the corn earworm is the key pest of sweet corn, European corn borer and fall armyworm are two other pests that sweet corn growers should be aware of  at this time of year.  The second generation of European corn borer (ECB) is now underway but it has been slow to start and is present at low density at all nine Ohio sites where we have traps. This pest will be infesting sweet corn as well as peppers. On sweet corn, ECB can be controlled by the spray schedule used to control corn earworm. On peppers, ECB can be controlled by insecticide sprays every 7 days. Fall armyworm (FAW) activity in recent weeks has been variable, with only a trace of FAW moths detected in traps in Columbus, Celeryville, and Wadsworth but FAW moths have been more abundant at South Charleston. Damage by fall armyworm is often most noticeable in whorl-stage corn but it can also be severe in silking corn.

Weekly catch of these three moth pests is shown on our online trap report page: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit?usp=sharing , where there is a tab for each pest along the bottom of the sheet.

More Ohio Counties with Cucumber and Melon Downy Mildew

Cucumber downy mildew

Downy mildew continues to take a toll on cucumbers and melons throughout the state. We have numerous reports of downy mildew on these two crops from northern and central Ohio, with new observations confirmed yesterday in Hardin and Greene counties.  Downy mildew is best managed by preventative fungicide applications – a list of effective fungicides can be found in my June 28, 2017 post.

We still have not confirmed downy mildew on pumpkins or squash anywhere in Ohio.  However, downy mildew has been reported on butternut squash in Blair County in central PA, and on jack-o-lantern pumpkins in Starke County, in northwestern IN.  It is a good idea to scout all cucurbits if you have not yet seen downy mildew in your area, and maintain a protectant fungicide program.  Keep in mind that on squash and pumpkins, powdery mildew can look like downy mildew in the early stages before the white powdery mycelium is seen.  Many of the fungicides used to manage these two very different diseases are fairly specific to either one, so be sure to have an accurate diagnosis.

Last Call – Pumpkin Field Day Aug. 17th

The Pumpkin Field Day will be later this week on Thursday, August 17th, from 6-8PM at the Western Ag Research Station in South Charleston.

Pumpkin plots at the research station.

This year’s field day will offer beginning and experienced growers valuable research updates regarding disease management, insect management, weed control, and showcase some new pumpkin and winter squash varieties.  Celeste Welty (entomology), Claudio Vrisman (plant pathology), Bryan Reeb (weed control), and Jim Jasinski (IPM Program and emcee) will be on hand to share their knowledge and answer your questions. There be presentations on how to identify and control weeds, insects, and diseases on this crop.

The field day will feature some traditional and new projects on the wagon tour, including a seven-treatment powdery mildew fungicide demonstration trial, a powdery mildew drip irrigation trial, a pumpkin variety trial with 20 hybrids ranging from small to large fruit, and a winter squash variety trial with 11 entries. This season has been marked by periods of heavy rain and cooler than average temperatures, resulting in a few hybrids that are a little behind schedule in terms of growth, having yet to produce any fruit. I anticipate by the field day they will have produced some fruit for you to see, although it may not be mature.

After the formal presentations, attendees will be encouraged to walk around the plots and interact with the specialists and other growers.

There is a fee of $5 per person; refreshments and handouts will be provided.

Pre-registration is requested by August 15th at www.surveymonkey.com/r/pumpkin17.

Here is the rough agenda for the field day:
5:30  Begin check in
6:00  Welcome, introductions, outline of field day
6:05  Board wagons and head to the plots
6:10  Orientation to plots, begin presentations
7:10  End formal presentations, begin plot walks
7:55  Board wagons, complete evaluations
8:00  Field day ends, travel safe!

See the preliminary flyer below for a few more details. Looking forward to seeing you there. Contact Jim Jasinski (jasinski.4@osu.edu) or 937-462-8016 for more information.

Pumpkin field day flyer.