Nematodes taking toll on cotton

Root-knot nematodes are already taking their toll in some West Texas cotton fields.

We have observed stunting associated with severe nematode populations in some fields. Stunting is occurring in fields that did not have a nematicide applied at planting and in fields that had a nematicide applied at-planting.

Presence of root-knot nematodes can be confirmed by digging up plant roots and examining the roots for galls. Root-knot nematode galls are formed when juvenile nematodes penetrate cotton roots and pierce the vascular cells. Feeding causes cells to enlarge and the knots or galls become apparent. This impairs root function by inhibiting the uptake of water and nutrients.

Management options vary depending on the level of nematode infestations. Crop rotation to a non-host is the best method in managing root-knot nematodes. Other options include seed treatments or Temik 15G applied in-furrow at planting followed by foliar application of Vydate C-LV. Planting partially resistant varieties is one of the most effective management options.

Beet armyworm

We have observed some beet armyworm damage in non-Bt cotton fields we are scouting. However, larval survival is low, with one larva surviving in some cases, but no larvae surviving in most cases. An insecticide application was not justified in these fields.

Young larvae will chew the green layer from the leaves, which causes a "window paned" appearance. We have reached treatable levels in some fields and are starting to see leaf and terminal damage. However, most of the fields have low thrips pressure or are growing fast enough to out run developing thrips populations.

Monitoring fields closely will allow you to detect when seed treatments or at planting insecticides have run out. If you start picking up immature thrips, then at planting insecticides or seed treatments have likely run out. Treatments may be justified when you are averaging one thrips per leaf.

Timing is the most important component of foliar applications. If considerable damage occurs prior to treatment, you may have missed your opportunity to have the most effect. Once you reach 5 true leaves, treatments are probably not justified because there is enough leaf mass and you are likely safe from economic damage.

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