What to Do About Deformed Yams? Disease and Pest Control Measures for Growing Yams

Yam is a plant of the rootstock section of the Dioscoreaceae family, with nutrient-rich and delicious tubers. In recent years, with the adjustment of the agricultural industrial structure, the planting area in Yanzhou City has increased year by year, bringing considerable economic benefits to farmers. However, during yam cultivation, internal tissue structure changes often occur due to adverse environmental conditions, cultivation measures, management methods and other factors, causing deformities in the yam during growth, such as branching at the upper end of the tuber, branching at the lower end, snake shape, flat-head shape, foot-sole shape, gourd shape, pockmarked shape, etc., which seriously affect the commercial performance and internal quality of the yam, cause reduced yield and declining benefits, and dampen vegetable growers' enthusiasm for planting. To this end, through extensive in-depth field investigations and field trials, checking data and conducting analysis, we have basically clarified the causes of yam deformities in the southwestern Shandong region and put forward some targeted control measures.

1. Causes of formation

(1) Influence of foreign matter in the soil. When backfilling the yam trench, hard objects such as stones, bricks, gravel and clods of clay mixed in the soil were not carefully removed or fully crushed, causing the yam tuber to encounter hard objects during growth, so the growing point was blocked and changed its growth direction, forming various deformities such as branching and flat-head shape.

(2) Blind application of seed fertilizer. When planting yams, in order to make the seedlings strong and grow rapidly after emergence, vegetable growers indiscriminately apply various kinds of seed fertilizer before placing the yam setts after opening the trench. As a result, because too much seed fertilizer was applied or it was not fully and evenly mixed with the soil, the setts came into contact with the seed fertilizer when placed, burning the buds and growing points, and producing deformities such as tuber branching and multiple heads.

(3) Application of undecomposed organic fertilizer. Yam has a relatively long growth period and needs a continuous supply of fertilizer to ensure normal growth and development. Therefore, when planting, it is necessary to apply heavily organic fertilizer with a long fertilizer effect, such as barnyard manure, compost, human excrement and urine, and cake fertilizer. These organic fertilizers should be fully fermented and decomposed before being applied to the field, but some vegetable growers, in order to save time and effort, directly apply manure transported from livestock farms or undecomposed human excrement and urine into the soil. After these undecomposed organic fertilizers are applied to the field, they still undergo a fermentation and decomposition process. The heat generated during fermentation easily damages the yam root system, tubers and yam setts, commonly known as "scalding the roots." In particular, the tissue cells at the tip of the tuber are tender and constitute the growing point of the entire tuber. When they encounter undecomposed organic fertilizer, they are very easily burned, affecting nutrient absorption and producing snake-shaped, gourd-shaped and other deformities.

(4) Damage by underground pests. When planting yams, no insecticide was spread in the yam trench to control underground pests. Pests such as wireworms, white grubs, mole crickets and root-knot nematodes can harm yam tubers throughout the entire growth period, such as biting and cutting off growing points, so that the yam tuber cannot elongate normally, causing yam deformities.

2. Control measures

(1) Carefully remove foreign matter in the trench. Manual digging of the yam trench should be carried out before winter, so that through winter and spring rain and snow erosion and freezing and weathering the soil clods are thoroughly crushed. When backfilling the trench, carefully remove hard objects such as stones, bricks and gravel from the soil, and do not fill large clods of soil into the trench.

(2) Apply decomposed organic fertilizer. Human excrement and urine, compost, barnyard manure and miscellaneous fertilizers are all complete fertilizers rich in nitrogen, phosphorus, potassium and various trace elements. Take advantage of the favorable opportunity of high temperatures in summer and autumn, when fermentation and decomposition are easy, to compost them in advance. Never directly apply raw fertilizer into the soil and cause the "root-burning" phenomenon. It is recommended to spread the well-decomposed organic fertilizer and part of the chemical fertilizer on the bed surface between two rows of yams after planting the yams, then rake once so that soil and fertilizer are evenly mixed and cultivated on both sides of the ridge.

(3) Strictly follow the planting technical regulations. Do not apply seed fertilizer before placing the yam setts in the planting trench. Underground pests can be controlled with a 30-fold dilution of 90% trichlorfon crystals mixed with roasted fragrant soybean cake crumbs, or for every 667 sq m use 4 kg of root-knot killer and 3-4.5 kg of fenamiphos mixed with 30 kg of fine soil and evenly broadcast in the sowing trench, then rake once with a hoe so that the pesticide and soil are fully mixed, then pour a little water along the trench. After the water seeps in, place the setts and cover with soil to form ridges, which can effectively reduce damage by underground pests such as mole crickets, white grubs, wireworms and nematodes. Never use pesticides blindly or arbitrarily increase the dosage. Adopt crop rotation to reduce the accumulation of nematodes at the base of yam stems in the soil. Yam is a vegetatively propagated crop, and during cultivation it is mainly produced year after year using yam setts. Continuous use of yam setts year after year easily causes decline in vitality and reduced stress resistance, resulting in varietal degeneration and deformities. In production, yam setts should be renewed and rejuvenated in a timely manner, with every 3-4 years as 1 cycle, using yam bulbils to re-propagate setts or using yam segments to renew the yam setts 1 time.