Western Cotton Specialists Weigh In On Planting

With planting underway and small seedlings emerging across the state, it is important to remember there are many things that can occur in the field affecting the survivability of those seedlings. Among those is seedling disease. Disease pressure can have a negative impact on seedling emergence and survivability, reducing stand and sometimes resulting in replanting.

The two main seedling diseases in Arizona are caused by the pathogens Rhizoctonia solani and Thielaviopsis basicola. The diseases associated with these pathogens are more commonly known as Rhizoc, damping off, soreshin and black root rot.

Seedling disease associated with Rhizoctonia is typically observed under cool soil temperatures that slow cotton seedling emergence and development, making the seedling more susceptible to infection. Black root rot is also associated with cool soil temperatures but is commonly observed under wet soil conditions.

Many commercial seed treatments can help mitigate the incidence of both diseases, but the most effective technique for reducing seedling disease risk is to plant under optimum conditions. Minimum soil temperatures of greater than 60 degrees Fahrenheit will speed emergence and seedling development, thus mitigating seedling disease pressure. A favorable, warm three-day weather forecast is also important to help avoid seedling disease issues.

Once the crop is established, look for any additional symptoms of young plant die-back — resulting in stand loss — in plants that are in the growth stage range of three or four true leaves up to 10. This is the most common time to observe symptomology associated with Fusarium oxysporum vasinfectum race 4. Even though the FOV4 fungus has not been documented in Arizona, it has been found in west Texas, eastern New Mexico and been a problem in California for many years.

If you observe young plant symptomology, please contact your local University of Arizona county Extension office for further instructions on collecting samples for analysis. Plant disease caused by FOV4 is not something we want to get a foothold in our production systems in Arizona. Your diligence in observing and reporting is appreciated. For more information on this and other cotton-related topics, go to cals.arizona.edu/crops. rnorton@cals.arizona.edu

The California winter leading up to cotton-planting season has been an unusual one, with above-average temperatures and a very dry December, January and February.

Many growers were restricted or uncertain about available irrigation water because up though early March, they hadn’t seen much winter rain or snow in the mountains to help replenish soil profiles. This resulted in preplant irrigation amounts being reduced in fields planted to cotton as well as other crops.

In addition to being drier than normal, increases in other crop plantings, including safflower, vegetables, trees and vines, mean cotton is in competition with “neighboring crops” that may be different than in past times. Under relatively dry winter/spring conditions, pressure from certain pests, such as lygus, may be lower than in wet years, which is a good thing.

However, the crop mix near cotton fields can also alter the cotton pests and beneficial insects you end up with. We still need to treat for pests and adjust treatments based on the mix of beneficials and pests residing in fields. Field scouting and the ability to adjust treatment options are always important.

At planting, wait for good, solid five-day heat unit forecasts available at ipm.ucanr.edu/WEATHER/index.html or https://cottoninfo.ucdavis.edu) combined with acceptable soil temperatures. Check carefully for early season insect and seedling disease problems, and check upper soil moisture relative to rooting depth when trying to diagnose early season stand and vigor issues.

In years with limited supplies of high-quality irrigation water, there may be some need to use some lower-quality, higher-salinity water supplies on cotton ground since it is quite salt tolerant. Cotton plants are most sensitive to high-salinity soils and irrigation water at seedling stages.

If possible, don’t start the season with the lowest quality water. If you use a more saline water and also have to reduce irrigations, plant growth and yields can be affected by combination stresses produced by delayed irrigations/water as well as salt accumulations.

Cotton’s relatively good salt tolerance can be of benefit; however, keep in mind that salt management and rootzone salt and trace element monitoring will become more important to long-term productivity maintenance. Minimal soil testing is needed to track soil chemistry changes occurring with longer-term use of these water supplies. rbhutmacher@ucdavis.com