As the summer progresses, the need for pest control actions becomes more important and berry growers should fine-tune their integrated pest management programs to prevent fruit losses and income due to pest and disease problems typical of the pre-harvest season.

During the past week, the harvest of major small fruit crops like strawberries and blueberries continued without major problems. However, typical summer weather conditions have arrived and with them high temperatures and rains have increased the need for crop protection against fruit rots and insect pest problems both in strawberries and blueberries.

In west central Michigan, daily maximum temperatures during the previous seven days (as of July 9, 2013) fluctuated between 64 and 84 degrees Fahrenheit. The maximum daily average was 79 F and the minimum around 64 F. In addition, there has been precipitation that, in some places, reached an accumulation of 0.5 inches of rain. High temperatures from the past several days had an effect on the length of strawberry harvest because these conditions accelerated fruit ripening, shortening the harvest season. Currently, the renovation of early season strawberries is in progress.

Regarding pest problems affecting strawberries, the appearance of spotted wing Drosophila (SWD) around Ottawa County strawberry fields has been limited to a single detection, but growers are prepared to deal with this problem by destroying unharvest fields and maintaining their chemical control options handy.

Blueberries, on the other hand, are being harvested at Allegan and Van Buren counties, and this week the harvest will start in Ottawa County. It is important for Michigan State University Extension to remind growers that keeping an active monitoring program to prevent infestations by SWD at harvest time ensures no fruit will be rejected or downgraded upon arrival at the packing plant. However, care needs to be taken when spraying chemicals onto the crop under high temperature conditions. Some of the products we are using for pest control, both insecticides and fungicides, are affected by environmental conditions prevailing during the time of application. Temperature effects may vary depending on the type of chemical and the tank-mix being applied on the crop.

High temperatures are an important factor when selecting the insecticide to use at harvest time against SWD. Both pyrethroids and some organophosphate insecticides like Malathion are negatively affected by high temperatures at the time of the application. In the case of the pyrethroids, their control effectiveness can be reduced from several days to a few hours. According to “Hot Temperatures will Ipmact Soybean Aphids and Insecticide Control,” effectiveness of pyrethroid insecticides such as Asana XL (esfenvalerate), Baythroid XL (beta-cyfluthrin), Delta Gold (deltamethrin), Mustang Max (zeta-cypermethrin), Ambush or Arctic (permethrin), or Warrior II (lambda-cyhalothrin) decreases as temperature increases.

The same is true for Malthion, one of the main tools for SWD control in small fruits. As a result of high environmental temperatures, Malathion sprayed on strawberries decreases to 2.70 percent of the initial concentration within two days of application, 0.93 percent after three days and 0.50 percent within seven days (see Malathion Technical Fact Sheet for more information).

Also, the tank-mix is another issue. Mixing fungicides and insecticides to control insects and fruit rots at harvest time may produce some unexpected results like inactivation of the insecticide or phytotoxicity to the crop. This season, we already have seen some fields with foliage damage after the application of a mix of insecticide, foliar fertilizers or fungicides when temperatures are above the 80s. However, with daily temperatures below 80 F, such mixtures may not have any effect on the crop.

Our main recommendation to prevent pest control failures or chemical damage to the crop is to pay close attention to the label. Read the label! It does not matter if you are familiar with the product you are spraying. Every year, labels are updated with new information on the use of the product. Thus, it is important that you take in consideration those changes when using these pest control tools.

If you have problems with your insecticide applications during harvest time or you are not sure about the tank-mix you would like to use, visit your local MSU Extension county office or contact Carlos Garcia at 616-260-0671 or garcias4@msu.edu.