Evaluation of several approaches to manage Meloidogyne incognita and cotton seedling disease complexes in the High Plains of Texas

Field experiments were conducted for control of the southern root-knot nematode (Meloidogyne incognita) and cotton seedling disease fungi (primarily Thielaviopsis basicola) in one naturally infested field during 1999 and 2000 and in three additional fields in 2000. Treatments included: seed-applied fungicides (triadimenol + mefenoxam + thiram and carboxin + PCNB + mefenoxam), cultivars (Paymaster [PM] 2326 RR and PM 2200 RR), and a nematicide (aldicarb at 0.83 kg a.i/ha). Plant stands were higher (P = 0.02) in the presence of aldicarb (77% emergence) than in its absence (74% emergence). Hypocotyl disease symptom ratings were lower (P = 0.0001) following triadimenol + mefenoxam + thiram seed treatment (0.53) as compared with carboxin + PCNB + mefenoxam (0.93). Root necrosis was lower (P = 0.002) following triadimenol + mefenoxam + thiram seed treatment (27%) as compared with carboxin + PCNB + mefenoxam (34%). In one field, in both years, aldicarb was associated with more root necrosis (58%) than in its absence (46%) (P = 0.004). At three other sites aldicarb did not affect root necrosis. Population densities of Meloidogyne incognita eggs and juveniles at midseason were greater (P = 0.005, P = 0.003, respectively) on PM 2200 RR (less resistant) than on PM 2326 RR (more resistant). Yield was affected by the plant genotype by aldicarb interaction (P = 0.02) but not by seed treatments. Aldicarb effect on yield was dependent on cultivar, whereas affect of seed treatment on root health was consistent and independent of cultivar and aldicarb. No conditions were identified when use of triadimenol + mefenoxam was detrimental.