Too little or too much rainfall has consequences that are very numerous and complex, and there is no cookie-cutter approach to dealing with the consequences.
For those dealing with too much rainfall in the Northeast, here are some of the consequences of excess rain followed by recommendations on how to minimize the long-term effects of a soggy spring.
Too much rain, especially if delivered in frequent showers, causes a number of problems for growers, including:
1. Poor transplant condition (e.g., “leggy,” or root bound), leading to difficult transplanting, poor and uneven stand establishment, or low vigor crops.
2. Increased seed and seedling disease, also leading to poor and uneven stand establishment and additional disease pressure.
3. Working wet soil, resulting in compaction and problems stemming from it.
4. Disruptions in scouting and the timely application of pest control measures, leading to increased pest and disease pressure.
5. Delayed or missed cultivation and/or herbicide inactivation, resulting in inadequate weed control.
6. Fertilizer leaching and runoff, leading to crop nutrient deficiency.
7. Waterlogged (and, possibly, compacted) soil, leading to shallow-rooted, low-vigor crops, that may be less resistant to other types of stress.
8. Disrupted planting and expected harvest schedules, leading to supply shortages and excesses.
Mitigating The Negative Impact Of Too Much Rain
Here are some pointers on how to minimize negative effects and outcomes of excess rainfall.
1. Maintain Transplant Condition
Slow transplant growth by lowering fertility, supplemental light, and, if possible, temperature levels (especially temperature levels during daylight hours). Maintain disease and pest control strategies in the greenhouse. Do not transplant vegetable seedlings with symptoms of bacterial diseases. Rainfall will move the bacteria throughout the field, potentially causing many problems later.
2. Decide If You Must Work Wet, Fine-Textured Soil
Using every rain-free minute most effectively is important. Balance short- and long-term objectives when deciding to work or not with wet fine-textured soil. Working wet, fine-textured soil this year may be useful now, but it will have significant, long-term, negative consequences that are difficult to reverse. Working some soils when they are wet can compromise their structure and lead to compaction. Compacted soils have numerous follow-on effects, including additional energy costs, limited internal drainage, minimal aeration, smaller root systems, and lower yield.
3. Reduce Seed And Seedling Disease
Fungal and bacterial seed and seedling diseases may reduce stand establishment and crop vigor. Re-planting with high vigor, short- or medium-season varieties may be warranted in extreme cases and fungicide-treated seed is nearly always recommended, especially in years where conditions are conducive to the development of seed and seedling disease. Increased early-season scouting is warranted. Pay special attention to disease management updates.
4. Keep Up With Scouting And Control Measures For Disease, Insects
When weather does not permit the application of crop protectants using ground equipment, little can be done to manage insects or diseases during cool, wet conditions. If crop values warrant, growers may want to consider aerial applications. Insecticide applications should not be made without verifying via scouting that the target pest is present. Even if scouting needs to be restricted to field edges, some scouting is better than none at all.
Heavy rains may sometimes eliminate pests such as aphids, mites, thrips, and small exposed caterpillars such as young European corn borer larvae. Damp weather is conducive to diseases such as Beauveria that can infect and kill insect pests.
Scout potatoes carefully for late blight, beginning at emergence. Check leaves and stems. If symptoms are found, destroy infected plants by removing them from the field and apply appropriate fungicides to the remaining crop immediately.
5. Cultivate When Possible And Watch For Herbicide Inactivation
Rainfall has mixed effects on herbicides; it may activate them further and/or leach them. Either way, cultivation and post-emergent herbicides may be needed later in the season to compensate for the lack of longer-term action. Cultivation should be attempted only when soil moisture permits, otherwise declines in soil quality (e.g., compaction) may offset potential gains in weed control.
Pay close attention to crop tolerance, application timing, plant back restrictions, and other label details when using any herbicide. Applying some herbicides during periods when growing conditions are poor (e.g., when there is excessive soil moisture or little sun and low temperatures) may damage some crops.
Do not use tank mixes unless they are specified on the label or cleared by a crop advisor or other trained personnel, due to potential antagonism or synergism.
6. Replenish Fertilizer Lost Due To Leaching, Runoff
Fertilizer lost to excess soil moisture can be replenished in several ways. Often a combination of methods is best.
First, fertilizer may be soil-applied in sidedress applications. A complete fertilizer may be used but expect a delay between fertilizer application and nutrient availability.
Second, nutrients may be foliar-applied, alone or in combination with crop protectants. This approach is best suited for nitrogen and some micronutrients but can be expected to deliver only a minor portion of total crop nutrient needs and often only indirectly (e.g., washing from foliage to soil). Pay special attention to materials and tank mixes in order to avoid burning the crop.
Third, nutrients (nitrogen, potassium) may be injected into irrigation water. Clearly, this method works best when soil moisture warrants irrigation. Which method(s) growers choose will depend on crop, soil condition, available equipment, and other factors. A crop’s appearance (e.g., color) is rarely a reliable indicator of its nutrient status. Therefore, post-planting fertilizer applications should be made in conjunction with sap or tissue tests whenever possible.
7. Minimize Future Waterlogging and Compaction Potential
Heavy rainfall compacts bare soil and promotes erosion and runoff. In the future, consider that both can be minimized by using plant residue mulches or other minimum tillage practices. Root channels and above-ground debris permit rapid infiltration, shield the soil from the impact of rain drops, and absorb moisture. Of course, these benefits must be balanced against the challenges of additional residue. Ways to minimize these challenges are being discovered and implemented by teams of researchers and farmers aiming to enhance the use of minimum-tillage approaches in commercial vegetable production.
Resources are available from SARE and from grower organizations and Extension. Clearly, tiling and other types of drainage improvement is also useful.