Vegetable Scouting Report: July 30, 2025

Alliums:

The second flight of the leek moth has ended or is coming to an end in most of the ENYCHP region where this invasive species is present. Damage to onions and leeks from the second generation is now evident, and the optimum timing for insecticide sprays has passed. To avoid leek moth caterpillar damage to onion bulbs during drying or curing, top onions up to 1” above the shoulders of the bulbs at harvest. UVM research has found that this practice does not have an adverse effect on bulb storage quality, and prevents lingering caterpillars in the foliage from traveling down to the bulb, and prevents the tird flight of leek moth from laying eggs on the onions.

Brassicas: Flea beetle populations are spiking again in some parts of the region and may cause issues on fall brassica transplants. Make sure to scout young plants in particular, and monitor more susceptible crops like radishes for severe outbreaks.

Cucurbits: Growers should continue to apply protectant sprays against Downy Mildew and should begin a spray program for Powdery Mildew at the onset of symptoms, which is likely to coincide with the main fruit set starting to size up on pumpkins. Cucurbit Powdery Mildew thrives in hot, dry conditions so it is also very important that you continue with fungicide applications.  Vivando tank mixed with chlorothalonil (Bravo, Initiate etc.) rotated with other fungicides in a different group like Procure, Provolio, etc. is important in order to allow fruit to ripen and mature before the plant succumbs to the disease.  See previous reports for links to complete control recommendations. Remember to terminate old plantings of summer squash as they come out of production, since they can be a reservoir for inoculum.  The same holds true for old cucumber plantings and Cucurbit Downy Mildew.  Pumpkins and winter squash fruit set is well underway in many locations and again, this is a critical time for water management.  If you have the ability and water availability to irrigate, during this stage of development is important.  Under severe drought and heat conditions, it is not uncommon for plants to drop their blossoms or in some cases even abort newly set fruit.  The hot temperatures also pose a problem for our bees as they tend not to travel as far from their hives.

Nightshades: Late blight continues to spread in Western NY.  Elizabeth Buck and Margie Lund from the Cornell Vegetable Program wrote up a great article on control strategies, which can be found here. Make sure that you are applying protectant fungicides to all tomato crops and either protect or terminate potatoes to prevent tuber infection. A complete table of available fungicides can be found here.

Leaf mold has been showing up in high tunnel tomatoes around the region, and some concerned growers have mistaken these symptoms for late blight after our latest reports of the latter disease in western NY. Leaf mold appears as yellow spots or mottling on the upper sides of tomato leaves, and when the leaf is turned over, brown fuzz (fungal growth) can be seen with the naked eye on the underside. Leaf mold is most easily prevented by growing resistant varieties. Several of our most popular tomato varieties, however, such as ‘Sun Gold,’ ‘Brandywine,’ and ‘Big Beef’ are NOT resistant to leaf mold. Good air circulation and avoiding leaf wetness can help prevent the spread of leaf mold. Several fungicides are labeled for use on field tomatoes, but products labeled for greenhouse use are limited. Copper sprays seem to have little effect on prevention of leaf mold spread. See ENYCHP emeritus Amy Ivy’s fact sheet on leaf mold for more information and a comparison of leaf mold versus late blight symptoms here.

Gray/Stemphylium leaf spot was found in a high tunnel tomato crop last week. Confirmed on Long Island in 2021, this fungal disease is relatively new to New York growers however, it may have been confused in the past as septoria leaf spot. The hot and humid environment in high tunnels favors the development of this foliar disease that occurs frequently in tropical regions. Peppers, eggplant and solanaceous weed species may also be infected. Spores are dispersed by wind and splashing water, carried on seed, and persist in crop debris.  Management strategies include reducing humidity (add fans, roll up sides, increase plant spacing and/or pruning), removing affected plant debris, and using resistant varieties. Some fungicides containing the active ingredient chlorothalonil are labeled for field use in New York, but for use in the high tunnel, the label must state that the product is allowed to be used on the specific crop and pest in the high tunnel to be a legal application.  Use of labeled products (such as the copper-based fungicide Badge X2) for other diseases commonly found on tomato grown in high tunnels such as early blight, leaf mold, and septoria may give incidental control of gray leaf spot.  More information and photos can be found by clicking here.

The last couple of weeks have also been prime conditions for Pith Necrosis.  The bacterium that causes this disease, Pseudomonas corrugata, can be found in all our soils and is favored by hot, humid weather with cooler night conditions.  The application of excess nitrogen is also a contributing factor for this disease.  Symptoms start out as wilting followed by large irregular lesions on the stems.  As it progresses, the stems become almost hollow and brown inside.  There is nothing you can do once the disease has started, but there are things you can do to reduce the incidence such as not pruning large suckers which can be an entry point for the bacteria, avoid working in the foliage when it is wet and be careful applying too much nitrogen.

Sweet corn: Western bean cutworm trap counts have been increasing steadily in the North Country, where we typically see the highest counts in our region. High trap counts usually do not result in large numbers of egg masses, caterpillars, and damage in the field, however. We have not yet observed eggs in the corn at our host trap sites in the north. The action threshold for WBC is one egg mass per 100 corn plants.  Corn in late whorl to early tassel is generally most appealing for WBCW and insecticide applications should target corn that is just starting to tassel, similar to European Corn borer management.  WBCW will also move into the silks and ears if not controlled at tasseling and like CEW, will become harder, if not impossible, once they enter the silks and ear tips. Often, spray schedules for other pests will manage WBC.

The storm fronts over the weekend brought in a whole new flush of Corn Earworms (CEW) – enough in many areas to continue to be on a 4 day insecticide spray program for corn in green silk.  Picnic or Sap Beetles along with Japanese Beetles also continue to be found regularly in sweet corn.  If you are using Coragen (chlorantraniliprole) alone, you will not control these pests.  Either mix in a pyrethroid with it or switch to a pre-mix product that already contains a pyrethroid like Beseige or Elevest.  There is also a fair amount of corn in the last couple of weeks that is showing some pretty severe drought stress which has taken its toll on ear size and pollination.  Silking to ear development is usually the most critical time for irrigation management, but if you have the capability and access to plenty of water, hitting corn in the early to mid whorl stage may also be beneficial.

Fall armyworm caterpillars have been observed feeding on corn despite no moths captured in traps. Unfortunately, this phenomenon has been the trend over the last few years, and we are unsure why the moths are not responding to the commercial pheromone lures. Weekly scouting is essential to prevent fall armyworm damage to sweet corn if a regular spray schedule is not already in effect. For tasseling corn, treat if >15% of plants are infested with caterpillars (fall armyworm + European corn borer) or show new damage. For silking through harvest, treat if >5% of plants are infested with caterpillars.

A small number of true armyworm caterpillars (a different species than fall armyworm) were observed in a North Country corn planting this week. We often see a few individuals of this species in sweet corn, causing a small amount of damage to plants but not enough to warrant treatment for this species alone.