Spring Cover Crops for Vegetable Rotations

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

One principle of managing soil for improved health is to always have a crop growing on the soil. This will maintain or add organic matter, provide benefits from the action of growing roots, and recycle nutrients.

Where fall cover crops were not planted due to late harvest, spring cover crops can be planted in early April to provide soil health benefits where vegetables and field crops are not scheduled until late May or the month of June.

The most common cover crop options for late March or early April planting include spring oats, mustards and annual ryegrass. Plant oats at 90-120 lbs per acre, mustards at 10-20 lbs per acre, and annual ryegrass at 20-30 lbs per acre.

Field peas are another option; however, we are somewhat south of the best zone for spring planting. One type of field pea is the winter pea which is often fall planted in our area but can be spring planted. It has smaller seed so the seeding rate is 30-60 lbs per acre. Canadian or spring field peas are larger seeded and used as a spring cover crop planted alone at 120-140 lb/A.

Mixtures can also be used. Field peas are well adapted to mixing with spring oats or with annual ryegrass. Reduce seeding rates of each component when using in mixtures. Recommended seeding rates are 70 lbs of oats per acre and 40 lbs/A of Austrian winter peas or 80 lbs/A of Canadian or spring field peas.

Many mustard family crops have biofumigation potential. When allowed to grow to early flower stage and then incorporated into the soil, they release compounds that act as natural fumigants, reducing soil borne disease organisms. Some biofumigant mustard varieties and blends include ‘Pacific Gold’, ‘Idagold’, ‘Caliente’, ‘Trifecta’, and ‘Kodiak’. Other mustard family crops serve as non-hosts, trap crops, or deterrents for pests. In research at the University of Delaware biofumigation using early spring planted biofumigant crops such as ‘Image’ radish, ‘Dwarf Essex’ rapeseed, or ‘Nemat’ arugula showed potential for managing root knot nematode populations. When used as a biofumigant, mustard family cover crops should be grown to achieve maximum biomass by adding 60-100 lbs of nitrogen per acre. Nitrogen is also required to produce high biomass with spring oats and annual ryegrass at similar rates. When planting mixtures with peas, nitrogen rates should be reduced.

An often-forgotten spring seeded legume crop that can also be used is red clover. Red clover can be frost seeded into small grains, seeded alone, or mixed with spring oats or annual ryegrass. Seeding rates for pure stands would be 10-16 lbs/A, for mixtures 6-10 lbs/A.

Spring planted radishes and mustards as cover crops.

Time to Scout for Cereal Leaf Beetle

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Begin scouting small grains for Cereal Leaf Beetles (CLB). Over the past few years, we have seen an increase in damage on small grains from cereal leaf beetle larvae. This past week’s Guess the Pest was a picture of adult cereal leaf beetle feeding injury. Adults feed on small grains (wheat, barley, and oats) causing longitudinal slits in the leaves. This damage is not a concern with the exception that it indicates you have adult CLB in your field, mating and laying eggs.

Cereal leaf beetle adult

Damage from CLB adult feeding

Larvae feed on small grain by removing the upper layer of leaf surface. Heavy infestations can result in significant yield losses by hindering the plants ability to photosynthesize. The damage can give a field a “frosted” appearance under heavy infestations. Once plants have reached the hard dough stage, CLB feeding injury will have no impact on yield.

Damage caused by cereal leaf beetle larvae.

Cereal leaf beetle eggs are about a 1/16th of an inch in length, orange and laid singly or in pairs along the leaf mid-vein. Larvae have a brown head and legs with a yellow body often covered with brown or black mucus and feces giving them a black, shiny appearance.

Cereal leaf beetle egg.

Cereal leaf beetle larva.

To scout for CLB larvae, examine 5-10 tillers in 5-10 locations throughout the field. Count the number of eggs and larvae per stem and estimate percent defoliation. The treatment threshold is 25 eggs and/or larvae per 100 tillers. Treatment is suggested when the threshold is reached and approximately half the eggs have hatched.

Research from Virginia and North Carolina determined that a growing degreed day (GDD) model is an accurate way to predict peak egg laying and larval hatch for CLB. Based on the model, we should be at peak egg laying throughout the state. However, keep in mind this model has not been validated for Delaware.

Here is a link to research published using the GDD model to predict peak egg laying and larval hatch:

https://projects.ncsu.edu/cals/entomology/sites/default/files/2012%20Philips%20et%20al.-%20DD%20CLB.pdf

See our Cereal Leaf Beetle Control in Small Grains Fact Sheet for more detailed information on CLB identification, biology, damage, management options, and threshold:

http://extension.udel.edu/factsheets/cereal-leaf-beetle-control-in-small-grains/

For chemical control options, follow the link to our Insect Control in Small Grains Recommendations Guide:

https://cdn.extension.udel.edu/wp-content/uploads/2012/05/18063827/Insect-Control-in-Small-Grains-final-2017.pdf