Of late, several regions in Kenya have received exceptional amounts of rainfall. The excessive rains will cause a variety of problems for farmers with the main headache being crops getting submerged in water.
The leaves submerged in water die off due to lack of oxygen. The floods also make the plants weaker because the plants cannot absorb nutrients.
If the soil is completely saturated for long, root loss can occur. Root cells in such soils cannot exchange gases and they can easily die. Root loss amounts can vary depending on the length of time the soil is completely saturated.
Total root loss
Total root loss would result in plant death and total crop failure. Partial root loss would result in lower plant performance and lower crop yields.
Wet conditions are breeding grounds for fungi because many fungal diseases require wet weather for the spores to germinate and survive. If crops are too wet, they could also start to mold or catch a fungus.
The soil can also start to collect bacteria, mold and fungus, which can then be absorbed by the plant. Rain can spread pathogens, pests, and other diseases to plants, leading to massive diseased crops.
This could affect its yield or cause the entire field to become unusable.
Tomatoes are affected by wet weather because it promotes the development of blight.
Kales start turning yellow. Monitoring the garden closely will let you find these problems quickly and you can begin to treat the plants before the problems become serious or fatal.
Leaching of nitrogen
Heavy rains will also cause leaching of nitrogen. Symptoms of such an attack include a yellowing of the lower leaves and gradually moving to the upper leaves. If the leaves have dark green veins with yellow between them, this is an iron deficiency and nitrogen supplements will not help.
To treat a nitrogen deficiency, add extra nitrogen in the soil. Should the rains continue, second application of nitrogen is recommended. Avoid over use of nitrogen as this will cause excessive green growth and reduced fruit set.
Wet conditions cause verticillium wilt in tomatoes. The disease requires cool weather and soil which is saturated for 24 hours. While infection can happen early, symptoms are seen later in the season.
Plants will start to wilt from the top down and watering will not perk them up. At the same time, lower leaves will yellow; mimicking nitrogen deficiency, and the inside of the stem will be discoloured.
To diagnose the plant, cut a large low branch off and look for chocolate brown discolouration in the vascular tissue. This discolouration is a clogging of the vascular system, specifically the xylem tissue which pulls water from the soil and moves it into the plant tissues.
Eventually the xylem becomes so clogged it can no longer carry water. If your plants are diagnosed with verticillium wilt, pull them out and either put them in the trash or burn them. Do not compost diseased plants.
Cool wet soils cause a number of stem and root rots. Soil that stays wet and does not drain has all the air spaces filled with water.
Adding organic matter to soil, especially clay soils will loosen it and allow water to drain.
Seeds planted deeply like corn, beans, peas and cucurbits will rot if the soil is saturated for more than a day or two.
Treat seeds with a fungicide before planting. To control stem, root and seed rot use the raised beds to elevate the planting surface.
Although we can’t stop all fungal infections and nutrient deficiency problems in cool wet weather, careful planning and monitoring of the garden will help to reduce them.
[The writer is an expert on sustainable agriculture and agricultural solutions]