Cold, wet soils and vegetable seed emergence
June 3, 2009 - Author: Dan Brainard, Michigan State University Extension, Department of Horticulture
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Cold, wet soils have contributed to poor stands of many vegetable crops this spring, and it appears that colder than normal temperatures will continue at least through the end of the week. Below are some common problems that contribute to poor stands under these conditions, and a few tips for avoiding them.
Cold soils delay emergence of vegetables and therefore increase the risk of losses due to soil-borne disease and insect pests. Many warm season vegetable seeds being planted now (snap beans, sweet corn, cucumbers) will take roughly to weeks to emerge at 60°F versus one week or less when temperatures get into the mid-70s. The longer the seed sits in the ground, the greater the risk of stand losses due to seed rots, seedling diseases and insect feeding since 1) pests have more time to attack their hosts and 2) seed protectants dissipate. Damping-off in carrots and seedcorn maggot in snap beans are among this spring’s examples.
Cold soils can also wreak havoc with weed management programs. Seeds of many weed species will stay dormant under cold temperatures, escaping pre-emergence herbicide programs. For example, in one of our trials involving stale seed beds in carrots, fewer weeds emerged than anticipated prior to carrot emergence, and our burn-down herbicide applications are likely to have missed many weeds. Under these conditions, a large flush of weeds may occur with crop emergence once temperatures increase. Heat loving weeds such as pigweed and purslane are particularly likely to lie in waiting until temperatures climb. At this point in the season, weed species that can germinate at cooler temperatures such as lambsquarters and smartweeds appear to be more dominant than usual in some fields, but this can change in a hurry.
While there is nothing that can be done about the weather, there are a few practices which can help reduce the risk of stand losses under these conditions. Delaying planting until temperatures increase can clearly be useful, although this may not be a practical option for many growers. Practices which encourage rapid emergence of seeds can also help including: 1) using high quality seed (tested in advance for germination and vigor); 2) planting on the shallow side; 3) planting into raised beds; and 4) using floating row cover (for high value crops). Longer-term strategies that can reduce the risk of stand losses due to cool, wet conditions include good crop rotation (to avoid build-up of pathogens and predators of seeds), and integration of practices which improve soil quality. For example, use of cover crops, and reduced-tillage practices can improve drainage, reduce soil crusting, and in some cases, reduce the pathogen load in soils. Studies with snap beans have shown reductions in root-rot when cover crops (e.g. oats) are incorporated and allowed to decompose before planting, and on-going studies with strip-tillage also suggest benefits for improving stands of snap beans and other crops.