The call of the week has been about spider mites in cotton. The hot, dry conditions are ideal for spider mites and worsens their potential impact on the crop. UT recommends treatment when 30-50% of plants are showing signs of injury and spider mites are still present. This may be too aggressive under low stress conditions, but most of the crop is currently under substantial heat and drought stress. I’ve previously commented about treatment options in cotton (link to previous article). There are a number of good miticides available. The most common choice for control is one of the abamectin products such as Agri-Mek, Zoro or Abba because they are relatively economical, and I would suggest a 6 oz/acre rate where treatment is needed. Other good options include Dicofol 4EC (32 oz/acre), Oberon 4SC (4-8 oz/acre), Portal (16-20 oz/acre) and Zeal (0.75-1 oz/acre).
By all means, treat when plant bug populations exceed threshold, but remember that making applications for plant bugs will aggravate your spider mite problem. So what if treatment for plant bugs is also needed? Unfortunately, none of the treatment options listed above will provide control of plant bugs. Because bifenthrin (e.g., Brigade) and dimethoate typically perform VERY poorly on spider mites this early in the season, you will be forced to tank mix if treatment for spider mites and plant bugs is needed. I think the best tank mix options prior to bloom are imidacloprid, Belay or Centric. Carbine and Intruder are other options.
You could consider tank-mixing one of the bifenthrin products with abamectin.* Athena is a premix of bifenthrin and abamectin marketed by FMC. Its use rate is 10 – 14 oz per acre. However, I normally discourage the use of this product prior to bloom because 1) the bifenthrin will not add much or anything to spider mite control and 2) I’m trying to save the pyrethroids until after first bloom to maintain their efficacy.
* Abamectin and avermectin are used interchangeably and is the active ingredient found in Agri-Mek, Zoro or Abba (among others). These products are not labeled on corn or soybean.
What about spider mites in other crops? Spider mites occasionally cause yield loss to other field crops including soybean and corn, especially when beneficial insect populations have been disrupted. This is yet another reason not to spray pyrethroids for no particular reason other than your “going across the field anyway”. But spider mites are not a common problem in either corn or soybean in the Midsouth. Treatment options in soybean are limited to Dimethoate, Lorsban or one of the bifenthrin products. Fortunately, these products tend to work more consistently in soybean than in cotton. There are a few other treatment options in corn including Comite, Oberon and Zeal. I will not go into treatment thresholds until an issue develops … but making treatment decisions is not easy. However, keep your eyes open.