Gordon Johnson, Extension Fruit & Vegetable Specialist; gcjohn@udel.edu
Vegetable crops are susceptible to a number of soil borne pests. In particular, soil borne diseases such as Fusarium in vine crops and solanaceous crops, Rhizoctonia in bean crops, Sclerotinia in bean crops, Verticilium in solanaceous crops, Pythium in most vegetables, and Phytophthora in vine crops, solanaceous crops, and bean crops have major impacts on the productivity of important vegetable crops in Delaware . Nematodes are also an issue on many vegetable crops in the state (root knot on many vegetables, lesion on potatoes as examples). Current control practices include fumigation and the use of soil applied fungicides or nematicides. However, the most effective control is the use of long rotations with non-host crops. This has been the standard extension recommendation to reduce the economic impact of these diseases and reduce the need for chemical controls. Long rotations are difficult to achieve on many farms due to land limitations. This problem has been worsened by the pressure of development and the decrease in farmland for rotations.
Insects and slugs in soils are also issues in many vegetable crops that affect overall plant heath. Often, as with the case of seed corn maggots, cutworms, and slugs; practices that are recommended to improve soil health – such as use of cover crops and no-till planting in vegetable production – can increase problems with these pests. This limits the adoption of these practices.
A major limitation to overall plant health in Delaware vegetables is soil compaction. Not only does compaction directly affect root growth, it also leads to increased problems with soil borne diseases as compacted soils often stay wetter for longer periods. In processing vegetables, harvest schedules often necessitate the use of heavy equipment and trucks when soils are wet, leading to extensive, deep, and long term compaction problems. Soil health is compromised and performance of future crops is affected.
Weed competition is another important issue in vegetable production. Management of the weed seed bank in soils can be a challenge and should be considered in an overall soil health program. Many vegetable crops have limited herbicides available to manage weeds and there has been an increase in the number of herbicide resistant weeds. Notably, herbicide resistant pigweed is a major problem in Delaware vegetable production. Adoption of soil health building practices such as the combination of cover crops with no-till and strip-till vegetable production is often limited by these weed control challenges. Weed control in organic vegetable production has also been a major problem limiting organic acreage.
Overall vegetable plant health is greatly affected by plant nutrition and soil fertility. Delaware requires nutrient management plans on all farms. Part of this planning process is how to incorporate best management practices to reduce nitrogen (N) and phosphorus (P) losses. Manure and compost use needs to be balanced against vegetable crop requirements and existing soil levels (for P) often limiting applications. On the other hand, practices benefiting soil such as the use of winter cover crops are encouraged as they can recycle nutrients (N primarily) that would be otherwise lost. While not directly related to management of a specific pest, decisions related to soil fertility and nutrient management will have implications for soil health in general, and therefore needs to be included in soil health and IPM program for vegetables.
Water management is directly tied to practices that influence soil health and vegetable crop performance. This includes ways to increase water holding capacities of soils; and at the same time, how to maintain good drainage and aeration. Improving soil water holding capacities will reduce vegetable plant stress and improve overall plant health. In addition, water management is linked closely with many soil borne pests, particularly in relation to drainage, with disease organisms such as Phytophthora being a major problem with vegetables in poorly drained soils in Delaware.
There has been a renewal of interest in soil health in relation to vegetable production in Delaware especially where tight rotations are an issue. Fortunately, there has been considerable research related to cover crops, green manures, compost, organic matter, and rotations in the past 10 years and there is ongoing research in the region on the effect of different rotations and species to improve soil health and reduce soil borne pests. Vegetable cropping systems that incorporate cover crops with no-till production or that have limited tillage have also been studied in the region. Other research in the region on cover crops that can reduce soil compaction is of great interest. There has been research on soil nutrient and water management for vegetable crops but limited work on how these areas intersect with soil health. Delaware vegetable growers, large and small, can benefit by adopting specific practices that improve soil health and by incorporating these practices into an integrated pest management programs for their farms.
Starting in 2009 and continuing into 2010, there has been a coordinated educational effort in Delaware on soil health as a part of integrated pest management for vegetables with field demonstrations, classroom sessions, publications, and on-farm training sessions. This initial effort emphasized how to evaluate overall soil health on a farm, the use of compost, general cover crop and green manure crop use, and biofumigant cover crops use.
We will be continuing these extension programs on soil health as a part of vegetable integrated pest management (IPM) programs over the next 3 years. In this effort we will expand educational areas to include soil disease management, soil insect and slug management, soil compaction management, weed management, soil fertility and nutrient management, and soil water management as part of an overall soil health and IPM program for vegetable crops. The emphasis will be on the on-farm adoption of soil health practices.
We are seeking 20 vegetable farmers as potential cooperators, targeting farms that are experiencing soil health problems and that have tight vegetable rotations. Plans to improve soil health in problem fields will be developed working with each farmer. This will include recommendations for rotations, cover crop use, green manure use, compost use, manure use, other organic matter additions, biofumigant crop use, and tillage practices. These prescriptive plans will be implemented by each farmer and the effectiveness of suggested actions will be evaluated at the end of 3 years by using soil health assessment tests (before the program starts and after 3 years). The economics of using these methods will also be assessed.
Delaware growers interested in participating in this program should contact Gordon Johnson, Extension Vegetable and Fruit Specialist, University of Delaware gcjohn@udel.edu, (302) 856-7303 office or (302) 545-2397 cell.