We finally have some rain, and there are decent chances in the forecast for the coming week. I swear a 0.5″ of rain is better than 1″ of irrigation.
Fertilizer: We have an interesting crop with May cotton blooming and June cotton just coming to square. Remember not to try to “catch up” with high N rates early for the June crop. This can cause problems as it will kick the plant into a vegetative state, and it won’t be able to shift into reproduction mode on time, which will cost yield. June cotton can’t afford a delay in fruiting. If you come up short on N later in the year for May or June planted cotton, you can foliar feed, especially anytime between the 3rd and 6th week of bloom. The beauty of foliar feeding N on June-planted cotton during “peak bloom” (first 4 weeks of bloom) is that foliar feeding N does not cause any vegetative or “rank” growth. The N goes right into the leaf, through the petiole, and into the bolls. Research studies have indicated this can all happen in about 24 hours. Leaching of K from the heavy earlier rains has been a big question this year. K isn’t as mobile as N, so I don’t think it’s completely gone, but it probably has been moved down in the soil profile. The heavy rains, I believe, have also compromised our root systems, so it may take some time for the roots to reach the K that you put out earlier. If you put all your recommended K out at planting and want to put some “extra” in at side-dress, that certainly is not going to hurt anything. Spreading KMag or Muriate at side-dress with your N may not be a bad idea. Still, if we get into the peak bloom period and start seeing a lot of K deficiency, we can also do some foliar feeding of K. Both N and K can be foliar fed together. One more thing: if you side-dress with Urea, I would think about urease inhibitors. Urease inhibitors are designed to “hold on” to the N for 10-14 days. Urea volatilization losses are probably somewhere around 10%.
Irrigation: It’s hot, so we really need to pay attention to evapotranspiration (ET). Look at the picture of the water balance calculator from the past 7 days. The picture of the UGA Bowen Farm Weather Station shows a negative water balance of -0.45″ for the past week, equating to the loss of about 0.05″ of water to ET daily. This isn’t bad, but we were losing up to 0.25″ a day in mid-June. So, the water you thought you were putting out may not have been enough. However, if you’re using soil moisture sensors, they indirectly account for ET since they are monitoring the moisture levels in the soil. A ramp-up in water use will occur sometime during peak bloom, usually around weeks 3-6 of bloom. It is important to monitor the crop and soil moisture moving into this stage and ensure that you do not fall behind on irrigation putting the crop into potential stress during bloom.
Flowering: Most of the early crops are flowering, which is a good time to gauge the plant’s horsepower. To gauge this, we look at nodes above white flower (NAWF) at first flower. First flower is reached when 50% of the plants in a field have produced their first white flower, which occurs roughly 60 days after planting. At first flower, NAWF values of 8-10 indicate a crop with high growth potential (lots of horsepower), while NAWF values of 3-5 indicate low growth potential (little horsepower). Low NAWF values can be attributed to crop stress. Peak bloom is when the rate of white flower production per day is at the maximum and typically occurs 2-4 weeks after first bloom. A plant with more horsepower at first flower will reach peak bloom later than a plant with low horsepower at first flower.
Insects: Aphids are spotty and late. We have not seen the aphid fungus yet, but we are watching for it. Usually, when we find the fungus in the field, aphid populations crash within a week.