Tomatoes planted in fields infested with tomato pests or fields with poor nutrient balance will suffer yield loss. Choose fields for tomato planting carefully, taking into account the field's cropping history. Also take into account pest problems that may originate in adjacent crops or fallow ground. Do these areas harbor pests of tomato such as root-knot nematode, potato tuberworm, or problematic weeds? Many weed problems can be reduced by not planting tomatoes in fields that are severely infested with difficult weeds such as nightshades, field bindweed, nutsedge, and parasitic dodder. If this is unavoidable, treat weed infestations before planting (see SPECIAL WEED PROBLEMS).
Use the information below when selecting fields for tomato planting. Well-chosen fields can result in fewer pest problems.
Assay Soil and Water
Identify Soil Type
Tomatoes can grow in a variety of soil types; however, deep loams and clay loams are preferred. Heavy clay soils require very careful water management and are generally less desirable. Sandier soils usually have higher root-knot nematode populations than soils that are more loamy. Avoid fields with large sandy streaks. Major variations in soil type within a field make application of herbicides difficult because rates must be adjusted for soil type. Drip irrigation can reduce irrigation-related management problems.
Nutrient and Mineral Levels
Check for excessive salt and boron, and other mineral imbalances. Soil electrical conductivity (ECe), expressed as deciSiemens per meter (dS/m), is used to measure soil salinity. Values above 4 are considered high and may require soil amendments. Boron levels greater than 5 ppm can also cause crop problems. In some Sacramento and San Joaquin valley soils, magnesium levels can be high enough to cause problems with potassium uptake.
Tomatoes grow best at pH 6.0 to 7.5.
Specific herbicide residues may inhibit seedling growth. Perform a soil herbicide bioassay if potentially damaging herbicide carryover is suspected.
Check Irrigation Water
If the quality of the irrigation water is unknown, assay for pH, salinity, nitrate levels, and specific ion toxicities. Irrigation water quality is also important for drip irrigation systems, as carbonates, iron, and organic matter can cause problems with filtration and clogging.
Assay for nematodes before planting tomatoes if they have been a problem in a previous crop. The best time to do this is in the fall when numbers are at the highest or spring before planting.
Determine the past tomato production history including planting and harvest dates and yields. See if the field has supported successful production.
Identify previous crops that are known hosts of tomato pests. Determine if pests such as garden symphylans, pinworms, potato tuberworm, nematodes, Fusarium or Verticillium wilt, and dodder or other weeds that might carry over to a new tomato crop, were present.
Surrounding crops and areas
Check for cultivated crops such alfalfa, cotton, or safflower that harbor lygus bug, which damages tomato fruit. Check alfalfa for armyworms, cutworms, darkling beetles, whiteflies, and tomato pinworm. If pinworm is found, get rid of solanaceous weeds in and around the tomato field that may harbor them.