Vegetable Crops Edition
Seasonal updates and alerts on insects, diseases, and weeds impacting vegetable crops. New Jersey Commercial Vegetable Production Recommendations updates between annual publication issues are included.
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EPA Publishes New Resources on Bilingual Pesticide Labeling (with editorial note)
What’s up with corn smut!
There have been numerous reports of corn smut throughout the state of New Jersey the past few weeks.
Corn smut (also called common smut), caused by Ustilago maydis, is found infecting corn throughout most of the world. In most years, corn smut is reported in New Jersey , but reports are limited to just a few plantings and just a few ears of corn. Corn smut gets its name from the sooty, black masses of teliospores that found on infected plants. Symptoms are tumor-like galls that vary in size from less than 1 cm to more than 30 cm in diameter. All meristematic tissues are susceptible to infection; and galls can develop on ears, tassels, stalks, shoots, and mid-ribs of infected plants (Pataky and Snetselaar, 2006). From the time of infection, it takes about 10 days for early symptoms to show up; followed up with a maturation of black spore masses within swollen galls about three weeks after infection (Figure 1).
Figure 1. Corn smut.
The fungus can overwinter as teliospores in crop debris or the soil and remain viable for many years. It is thought that the teliospores (i.e. the black spores – it is estimated that up to 200 billion spores are produced in a medium-size gall!) are unimportant in the summer they are produced, but more importantly act to overwinter and cause infections the next growing season (Pataky and Snetselaar, 2006) .
There is no general agreement on weather conditions that are most favorable for common smut, although most reports indicate that common smut is prevalent following rainy, humid weather (Pataky and Snetselaar, 2006). Galls on leaves and stalks of seedlings often are observed following strong thunderstorms with heavy winds, especially when plants are injured by blowing soil (Pataky and Snetselaar, 2006). Factors that reduce the production of pollen or inhibit pollination also increase the occurrence of ear galls of common smut. Thus, hot, dry, drought-like conditions often cause asynchronous pollen production and silk emergence which results in poor pollination and common smut may be prevalent if U. maydis is readily disseminated to stigmas of unfertilized ovaries during or immediately following these hot, dry conditions (Pataky and Snetselaar, 2006). Thus, some associate the occurrence of ear galls with droughts although the droughts probably affect the prevalence of ear galls primarily by increasing the number of unpollinated ovaries with rapidly growing silks (Pataky and Snetselaar, 2006).
Although there has been a great amount of research in controlling corn smut with fungicides (c0nventional and biological), adjusting fertility, crop rotation, sanitation, and seed treatments, the best management practice for limiting losses due to corn smut are planting smut resistant corn varieties (Pataky and Snetselaar, 2006). Although, none are completely resistant to the pathogen.
Unfortunately, for much of New Jersey this summer the weather conditions (the extended drought-like conditions in July) followed by the heavy isolated rains leading most likely to poor pollination periods and timing of corn smut infections led to the situation we are seeing now. Growers with significant smut issues might consider removing and destroying smutted ears to reduce inoculum loads, plan on choosing sweet corn varieties with resistance next year, and changing irrigation practices to help reduce crop stress during pollination periods.
References:
Pataky, J. and Snetselaar, K. 2006. Common smut of corn (Syn. boil smut, blister smut). Plant Disease Profiles, The Plant Health Instructor. Volume 6. <doi.org/10.1094/PHI-I-2006-0927-01>
For more detailed information on corn smut, it’s biology, and history please see the link to the following article referenced above by Jerald Pataky and Karen Snetselaar at The Plant Health Instructor Website hosted by APS.
https://www.apsnet.org/edcenter/disandpath/fungalbasidio/pdlessons/Pages/CornSmut.aspx
Neopestalotiopsis on strawberry is back
Neopestalotiopsis, a new disease on strawberry is back in the news. Please see the excellent article by Dr. Phil Brannen from the University of Georgia by clicking below.
Dramatic Neopestalotiopsis Disease in Strawberry Tips and Plug Plant Production Nurseries
Vegetable IPM Update 8/21/24
Sweet Corn
Fall armyworm (FAW) infestations continue in most scouted locations in central and northern NJ counties. There are pockets of heavier pressure, such as on the Burlington/Camden County border area. Re-infestations following treatment can and have occurred. Because FAW moths are highly mobile, it is important to monitor fields at least weekly for signs of infestation. Whorl, and even seedling stage plants are prime targets for egg laying. Delays in treating whorl stage infestations can lead to stunted plants and poor ear size.
Newly hatched FAW larvae cause holes and scratches on leaves that are similar to ECB feeding, except that they tend to be more concentrated and always lead down into the whorl (see photo at upper left). As the larvae grow, the feeding becomes more destructive, with large ragged holes and obvious droppings deposited in the whorl (see photo at right).
We will provide updates on new FAW appearances and severity as reports come in. FAW are resistant to synthetic pyrethroids. Effective sprays should include IRAC grp. 5 (spinosyns) or IRAC grp. 28 (diamides). The carbamate (IRAC grp. 1A) Lannate is also still effective. Sufficient water should be used in the applications to allow the solution to reach larvae that are partially protected while feeding on the immature tassel (photo at lower left), and to penetrate the layer of droppings that may have formed above the caterpillars.
Private Applicators: NJDEP August Mailing of 2025 Invoices & Recertification Credit Status
Cucurbit Downy Mildew Alert – Pumpkin and Summer Squash – 8/21/24
Cucurbit downy mildew (CDM) has been reported on pumpkin in central New Jersey (8/18) and on yellow summer squash and zucchini in southern New Jersey. These are the first reports of CDM on pumpkin and summer squash in the state and region this growing season. All cucurbit growers should scout on a daily basis and initiate a preventative CDM fungicide program immediately. CDM was confirmed on cucumber in New Jersey on 6/19/24. Remember, some CDM isolates fall into Clade I which predominately infect watermelon, pumpkin, and squash, where CDM isolates in Clade II predominately infect cucumber and cantaloupe.
For more information on CDM, the clades, and CDM control please click here.