Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
Double cropping season is here and many vegetables will be planted as a second crop behind barley, wheat, peas, early sweet corn, early snap beans, other spring vegetables, and even strawberries. The following are some considerations when double cropping vegetables.
● Crop residue management is critical in order to get a good seed bed for the double crop vegetable. Make efforts to spread and incorporate residue evenly. Heavy areas of incorporated straw or vine will lead to crop variability. Incorporation of high carbon materials such as small grain straw can lead totemporary nitrogen deficiencies. Therefore, extra nitrogen fertilizer will be needed to speed decomposition of these materials (green materials such as pea vines will not cause this problem and will rapidly decompose). It is advised to allow some time (minimum 5-7 days) for residue decomposition before planting the next crop. Allelopathic responses (toxic reactions) in the double crop planting have been found in certain cases when planting has occurred immediately after incorporation of residues.
● Pay close attention to herbicide plant back restrictions. Low rates (0.5-0.75 lbs) of atrazine are often used in sweet corn and this normally does not affect subsequent plantings. However, higher rates can damage the double crop planting. Mesotrione (Callisto), which is used in sweet corn, has significant replant restrictions to many vegetables as does Impact, a related herbicide. Command, Reflex, and Pursuit are examples of other common herbicides with significant plant back restrictions. Check the Delaware Commercial Vegetable Production Recommendation book and the specific herbicide labels for appropriate waiting periods and crops rotational restrictions.
● Some pest problems can be an issue in double crop plantings. Once a crop is harvested, some insects will be seeking a new food source and the newly emerging double crop planting can be at risk. Insects and mites may also move from field margins into the double crop planting. Grasshoppers and two-spotted spider mites would be examples.
● Herbicide programs should be designed to deal with any regrowth issues from the previous crop. Examples would be effectively killing plasticulture strawberries so that vine crops can be double cropped on the beds or dealing with spring brassica crops that went to seed as volunteer weeds.