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There are four nematode species that affect cotton yield potential. The most widespread and potentially the most damaging is the southern root-knot nematode (Meloidogyne incognita).1 The remaining three nematodes: reniform (Rotylenchulus reniformis), Columbia lance (Hoplolaimus columbus), and sting (Belonolaimus longicaudatus) are not as prevalent across cotton growing areas, but can also greatly reduce yield potential.
Nematodes reduce cotton vigor through root injury, which limits root growth and can increase the susceptibility to environmental stress, insect damage, and diseases, most notably Fusarium wilt.
Symptoms of nematode feeding are most noticeable when environmental conditions cause plant stress. Distribution varies, and soil type may increase the incidence of infestations. Southern root-knot and Columbia lance nematodes prefer sandy soils, but may also reduce yield potential in other soil types. Nematode presence may be likely if one or more of the following symptoms are observed: production of nematode-susceptible crops for two successive years, areas in the field with stunted plants that wilt by midday, and stunted roots with possible galls or enlarged root tips (Figure 1). Symptoms of nematode damage can resemble nutrient-deficiency due to damaged roots not having enough surface area to uptake adequate water and nutrients from the soil. Irregular growth in oval patterns may be observed in the field.2 Symptomatic plants may be carefully removed from the soil to determine the presence of below-ground symptoms (Figure 1). Soil sample analysis can determine nematode species and population.
Predictive soil sampling is essential to developing a nematode management plan. Nematode presence is typically highest around harvest; therefore, it is recommended to sample within one month prior to harvest, immediately after harvest, or after the last irrigation. Samples should be taken with adequate soil moisture. If low soil moisture conditions persist two weeks after harvest, sample immediately. Take samples at a 45° angle, six to nine inches deep and four to five inches from the plant. Targeting the root zone ensures the inclusion of root fragments, increasing the likelihood of collecting nematodes in the sample.3 As nematode distribution may be irregular, soil should be sampled in a random pattern, mixed together, and packaged according to assay laboratory directions. Sample size should be limited to 20 acres or less and segregated by soil type, drainage, and crop history. Lab results will estimate the risk of nematode problems for the following year’s crop.
Diagnostic soil sampling may be used throughout the growing season if nematodes are a suspected problem. Samples should be collected around the edges of symptomatic areas near the plant’s root zone when soils are not overly wet or dry. Nematode populations are often more concentrated along the edge of an affected area as healthier plants are able to support higher populations of nematodes.
Store samples at room temperature and out of direct sunlight to ensure nematode survival. Ice packs may be used to keep samples cool during transportation, but should not be in direct contact with samples. For best analysis, samples should arrive within one day of sampling.
Nematodes can not be eliminated from the soil, but it is important to keep populations at low levels to avoid potential yield and quality losses. Identifying nematode species and damage action threshold levels are essential for determining the appropriate control options. Nematode damage action thresholds may vary by species, soil type, and state. The following cultural practices may help growers reduce the impact from possible nematode infestations.
Incorporating cultural practices into a nematode management system may also be paired with the use of nematicides to help control nematode infestations. Nematicides may be applied in various ways including: seed treatments, fumigation, and soil or foliar application.
Acceleron® Seed Applied Solutions ELITE plus Poncho®/VOTiVO® can provide protection from early-season nematodes, insects, and diseases. This offering includes a biological mode of action to protect against southern root-knot, reniform, and Columbia lance nematodes. The dual insecticides provide broad-spectrum insect protection from black cutworm and early-season thrips and aphids. The fungicide combination protects against black root rot (Thielaviopsis basicola), Fusarium wilt (Fusarium oxysporum), damping off (Pythium spp.), and soreshin (Rhizoctonia solani), and also offers improved plant health through rapid emergence of seedlings under certain cold conditions.
Cotton growers may combine seed treatment nematicides with fumigants like Telone® II or a foliar-applied product like Vydate® C-LV to further suppress nematode development and feeding.6 However, chemical application timing and additional safety precautions may limit flexibility during the growing season.
AgLogic™ 15G is a granular aldicarb product that may be available to help reduce insect and nematode damage. AgLogic 15G is similar to Temik® 15G, which was widely used for effective control of thrips and nematodes in cotton. Both AgLogic 15G and Telone II are Restricted Use Pesticides; however, AgLogic 15G may be easier to apply and at a lower cost than Telone II.7
Cotton varieties with limited resistance to southern root-knot nematodes have been available to growers, but these varieties are only adapted to low populations of nematodes. New southern root-knot nematode-resistant (NR) varieties have been developed for moderately to highly infested fields. These NR varieties contain a native breeding trait found in cotton germplasm that not only resists southern root-knot nematodes, but also suppresses reproduction, leading to population reduction compared to planting a susceptible variety. This trait provides season-long protection for the crop. The NR varieties have been bred to combine high yield potential with southern root-knot protection whether in southern root-knot-free or infested fields. Variety selection may be the most effective way to reduce southern root-knot nematode damage (Figure 2).