Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Many Delmarva vegetable growers plant cover crops that winter kill. This reduces costs for crop destruction prior to planting early spring vegetables. With the mild January and February temperatures, many cover crops have not fully winter killed, including fall planted spring oats, forage radish, and some mustard species. For vegetable growers seeking to have early areas for spring planting, this will require that these cover crops be killed by non-selective herbicides or tillage. This will also limit the potential to plant no-till vegetables into these areas.
Radish cover crop that did not winter kill.
Another concern is with higher risk of seed corn maggot damage to early planted vegetables. The following is a reprint of an article from Joanne Whalen in 2016 on this issue with some additions regarding terminating cover crops in italics.
“Seed Corn Maggot in Spring Planted Vegetables”
Warm daytime temperatures in late February and March followed by cooler spring temperatures may result in very favorable conditions for seed corn maggot (SCM) infestations. Spring planted vegetables most susceptible to maggot damage include cole crops, melons, peas, snap beans, spinach, and sweet corn. SCM overwinter as pupae in the soil and adult flies start emerging in our area in late February and early March. SCM larvae (maggots) can cause damage by burrowing into seeds, cotyledons and the below ground hypocotyl tissue of seedlings. Maggots can also burrow into the main stems of plants.
There are other maggots that can attack spring planted crops; however, the SCM generally occurs earlier in the season and has the widest host range.
As most are aware, there are no rescue treatments for maggots, once damage is found it is too late to control them. Cultural control options to consider include: (a) avoid planting into fields where animal manure was recently applied and/or where a green manure was recently incorporated – this will be an issue with cover crops that did not winter kill; (b) early disking or plowing under of crop residues to ensure that they are completely decomposed before planting – this should take place 2-4 weeks before planting; (c) good weed management; and (d) planting seeds as shallow as possible to encourage quick emergence. Chemical control options can include commercial applied seed treatments, or soil insecticides; however, not all options are available for all crops. In addition, if conditions are favorable for seed corn maggot, a combination of a seed treatment and soil insecticide (where labeled) may be needed to provide effective control. Please refer to the Commercial Vegetable Recommendations for available control options. (http://extension.udel.edu/ag/vegetable-fruit-resources/commercial-vegetable-production-recommendations/)
Seed corn maggot damage to a pea seedling.