   Preventing Vegetable Pests - April 19, 2000 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Usually our vegetable gardening enthusiasm is great at soil preparation and planting time, then it slowly wains as various pest/disease problems appear and sap the energy from both plants and the planter. Many pest problems can be decreased or prevented if some simple steps are followed. Below are some ideas that you can try in your garden. Improving the soil and providing ample nutrients will ensure young plants get a strong start. A vigorously growing crop can tolerate higher levels of pest damage and better compete with weeds than a less healthy one. Changing your soil texture from a sandy clay to a loam is practically impossible, but improvements can be made through the addition of organic matter and fertilizers. Four inches of well rotted compost turned into soil will increase water holding capacity of sandy soils, drainage and aeration of clay soils, add some nutrients and attract beneficial soil organisms such as earthworms and microbes. Nitrogen and phosphorus are the most critical nutrients needed for annual vegetable crops. Personal preference will determine whether you use organic of inorganic fertilizers. In either case, only a portion of the nitrogen and all of the phosphorus should be added to the soil prior to planting. Organic nitrogen sources include manure, blood meal, hoof and horn meal, fish products, cottonseed meal, and many others. Manures contain varying levels of nitrogen and can contain pests such as root maggots, green fruit beetle, and weed seeds. It is best to apply uncomposted manure to the soil surface a month or so prior to planting and irrigated to begin decomposition. Inorganic nitrogen sources are inexpensive and easy to obtain. Here, care must be taken to avoid over application. Applying organic phosphorus is more difficult. The phosphorus in bone meal and rock phosphate is not readily available to plants. Whether using organic or inorganic sources, phosphorus fertilizers should be placed directly under plants where the roots can grow through them. Proper irrigation can also reduce pest problems. Too little water will cause slow growth and poor root development. Stunted plants are more susceptible to root knot nematodes and other harmful agents. Excessive irrigation can contribute to root disease problems. Uneven irrigation can encourage weeds and prevent uniform maturing of the crop. Some crops respond to uneven watering by decreasing the edibility of the crop. For example, cucumbers become more bitter when soil is allowed to dry completely between irrigations. The method used to apply irrigation can also affect the incidence of garden pests. Many commercial producers overhead (sprinkle) irrigate from planting to thinning, then switch to furrow irrigation for the rest of the season. Overhead irrigation is not good for mature plants. Soil can splash onto leaves and the chance of foliar diseases is increased. Drip irrigation products are very efficient and improved products are available from suppliers. Drip systems can be used in combination with row covers to warm the soil and speed early crop establishment. Pest and/or disease resistant varieties are now available for many crops. If you know of a specific pest in your garden area, look for varieties that are resistant (tolerant). Rotating where certain crops are planted can also reduce pest problems. This is especially critical where root knot nematodes and root diseases are present. Where soil borne diseases persist, soil solarization can reduce or eliminate these pests. To solarize soil, put a clear plastic sheet on the soil surface for four to six weeks during the hottest part of the year. Put a thin layer of soil on the edge of the tarp to prevent it from blowing away. To repel aphids and whiteflies, use an aluminum foil mulch when plants are small. These become less effective as plants mature. Row covers provide a physical barrier against insect and animal pests. Cages can be constructed from scrap materials and covered with a variety of materials to exclude a variety of pests. Insects can be excluded by covering cages with muslin or nylon. Large garden pests can be excluded by using screen. The University of Arizona Cooperative Extension has publications and information on composting and fertilizers. Visit our county web site at http://ag.arizona.edu/yavapai/. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |