Cotton: The crop ranges from 4 leaf to the second week of bloom. It does not take long for dry conditions to take over. Irrigation requirements increase as the crop approaches bloom. The UGA Weather station at the Sunbelt Ag Expo reported evapotranspiration rates from 0.23 to 0.26 inches per day for 6 out of 7 days last week. There is rain in the forecast for the first part of the week.
The UGA Irrigation Team had a great article in the July Edition of the UGA Cotton Team Newsletter. Below is a part of the article that discusses a couple of key points about cotton irrigation in July.
Cotton that was planted during May in Georgia should be squaring by now and approaching bloom, if it hasn’t already began blooming. Bloom occurs roughly 9 weeks after planting and water requirements really ramp up and approach peak demand during this time. Irrigation requirements and demand are very critical during the “First flower to first open boll” period of development. This growth stage takes place during weeks 9-17 after planting. Thus, based on when your cotton was planted, you will probably enter peak demand during the month of July. During this stage, cotton may require up to 1.5 inches per week or 0.2 inches per day. Keep in mind that the Soil Water Holding Capacity of most of our soils is around 1.0 inches/foot of soil. The crop can only access water where it has roots and of this SWHC only about 50% of it is plant available. Thus, a cotton plant with an 18-inch rooting depth will have access to 0.75 inches of water at field capacity, meaning it will require irrigation every 3 to 4 days minimum based on rainfall and irrigation efficiency during this stage. It is important not to let your cotton crop experience water stress during the flowering stage, as stress during this stage can reduce plant growth which in return can reduce the number of fruiting sites that are initiated.
The dry weather has made a good environment for spidermites. Apply when 50% of plants are symptomatic and populations are increasing. Spot treatment may be adequate. Thorough coverage is essential; a second application may be necessary. As the crop goes into bloom and stinkbug applications go out, insecticide selection will be important to not flair populations. According to the UGA Pest Management Handbook control options include abamectin, Zeal and Portal. Bifenthrin may provide suppression of mites. In fields where mites are observed, conservation of beneficial insects should be a priority; insecticides prone to flare mites should be avoided when targeting other pests. It you are interested in reading another good article from UT Extension about spider mites you can read it here.
Bacterial blight: Last week, I ran across a couple of fields with low levels of bacterial blight in DPL 2141. According to Dr. Bob Kemerait, conditions earlier this season have been favorable. Nothing can be done except hope it doesn’t get too bad. According to the UGA Cotton Production Guide, the single most important and effective way to manage bacterial blight is to plant a more-resistant variety and to avoid planting susceptible varieties. More information about bacterial blight and cotton varieties is included in the UGA Cotton Production Guide.
How do I control bermudagrass in cotton? I have received this question several times this week. For success, fall applications are needed. At least 7 days before frost, apply Roundup at 2.25 lb a.e./A in single application or two applications 7 days apart at 1.13 lb ae/A. During the following season implement both Roundup and postemergent graminicides when feasible. Postemergence graminicides (Select, Select Max, Fusilade DX, Assure II) are effective options when bermudagrass has runners less than 6”; however, a tank mix of Roundup plus a graminicide would likely be the most effective option when labeled. (Source: UGA Cotton Production Guide)
How do I control nutgrass in cotton: The most effective system will include sequential applications of Roundup applied topically with applications 7 to 10 days apart just to hold the nutsedge in place followed by a layby mixture of glyphosate or MSMA plus Envoke (0.15 oz/A) plus diuron or Caparol; it is the layby application that ultimately controls most of the population. Although Liberty and Graxmone provide a visual perception of control, they usually are not an effective option. (Source: UGA Cotton Production Guide)
Peanuts: The peanut crop ranges from 3 weeks to 70 days old. It does not take long before it gets dry again. Irrigation requirements for 60-day peanuts are 0.23 to 0.25 inches per day. According to Wes Porter, UGA Irrigation Specialist, most soils in Georgia hold about 1 inch of water per 1 foot of soil, and peanuts cannot extract more than 50% of the soil water. One concern is shallow-rooted peanuts due to the wet weather. The caterpillar situation has been quiet over the last few weeks. The treatment threshold for combined foliage feeders is 4–8 per foot of row, depending on the size and condition of the peanut plants. Use a lower threshold for very young plants or plants that are stressed from other factors. Use a higher threshold for healthy plants with ample vine growth. I have been finding low levels of lesser corn stalk borers in sandier peanut fields.
I thought this was interesting this week. The white mass is a cluster of pupal cases (cocoons) of the Cotesia wasp. The tiny parasitic wasp lays its eggs in a caterpillar. The eggs hatch and the wasp larvae feed on the still-living host. The larvae emerge from the caterpillar and spin the silken cocoons, where they complete their development before emerging as fully formed adults. The picture below show the pupal cases of this parasitic wasp.
Below is picture of “false white mold” in peanut field. Most often occurs in conservation tillage. May scare the growers but causes no harm. False white mold is caused by the fungus Phanerochaete, false white mold initially looks nearly identical to the REAL white mold, but later becomes more yellowed and with a ‘toothed’ appearance. False white mold blankets the peanut limbs but does NOT cause injury.
Pink purslane control in peanut!! I had this question a couple of weeks ago from a consultant about controlling purslane in peanut. Dr. Eric Prostko, UGA Weed Specialist, sent this information out to County Agents over the weekend about this subject.
Pink purslane has been a bur under my saddle for many years. Consequently, my PhD graduate student (Nick Shay) is conducting POST control studies as part of his dissertation. Nick already completed 2 trials in the greenhouse last fall and 1 field trial this summer. The following are the recent results of the field trial that he conducted. Surprisingly, only Aatrex (atrazine) and Cobra (lactofen) were effective in this POST trial. This field trial will be repeated again later this summer.
Corn: The corn crop ranges from blister to 1/2 milk line. Corn irrigation needs to be terminated when the crop reaches black layer stage of development. Early irrigation termination on corn is a common mistake and it can hurt your yield depending on when you cut the water off. Although kernels outwardly appear mature and corn water use begins declining at the dent stage, this is far too early to terminate irrigation. Potential kernel weight is only about 75% complete at the dent stage. Thus, termination of irrigation at the dent stage can reduce grain yields as much as 15-20% when hot, dry conditions persist. Early irrigation termination will also likely reduce stalk strength and promote lodging, because plants will cannibalize energy from vegetative organs to fill kernels when they are stressed. So water corn until black layer…
I have been receiving questions about checking milk line in corn. Corn kernels mature from the outside-in when hard starch forms beginning at the top of the kernel at dent and steadily progresses towards the base of the kernel (where it attaches to the cob). This final stage of grain development normally takes about 20 days to complete. The most reliable method for you to monitor kernel maturity for irrigation scheduling purposes is to observe this progression of the milk-line (or hard starch layer) between dent stage and black-layer or physiological maturity. The milk-line is more relevant than the black-layer, because it indicates maturation progress, before the black layer is evident. The milk-line is the borderline between the bright, clear yellow color of the hard seed coat outside the hard starch, compared to the milky, dull yellow color of the soft seed coat adjacent the dough layer. To observe the milk line, break a corn ear in half and observe the cross-section of the top half of the ear (the side of kernels opposite the embryo). If you have difficulty seeing this color disparity between layers, you can find it by pressing your fingernail into the soft, doughy seed, starting at the kernel base and repeating this procedure progressively toward the tip, until you feel the hard starch. The photo below shows about 1/3 milk line.
If you have questions please contact you local county Extension agent.
Have a great week.
Jeremy M. Kichler
Colquitt County Extension Coordinator
The University of Georgia Cooperative Extension does not endorse or guarantee the performance of any products mentioned in this update.