Extension of Spray Season due to Brown Marmorated Stink Bug
As we are getting through the peach season and starting our early apple harvest, codling moth sprays are done and most growers would prefer to put the sprayer away soon like they did in the good old days before that troublesome Asian pest known as the Brown Marmorated Stink Bug (BMSB) came along. This pest not only caused a lot of damage for many growers, but extended our spray season right up through harvest time. It made us start to look up re-entry and pre-harvest intervals more than we used to and it brought the first wide-spread use of pyrethroids to Pennsylvania apple orchards. Pyrethroids were always a bad word in Pennsylvania IPM programs because of the negative effects they have on the biological control of secondary pests such as spider mites, woolly apple aphids (WAA) and San Jose scale (SJS). BMSB also brought the return of harsh broad spectrum insecticides like Lannate, Thionex and Diazinon that we hadn't used much since the days when tufted apple bud moth (TABM) was the main pest of concern in our apple orchards. Since the IGRs Confirm and Intrepid made that pest mostly a memory, we have seen some relatively minor flare-ups of mites and woolly apple aphid for a couple of years after the introduction of some products like Assail and Delegate. For the most part, however, our biological control agents either began to tolerate the new products or, in the case of Delegate, we learned to use it earlier in the season for 1st generation codling moth when it did not impact the predatory mite, T. pyri, or the parasitic wasps and flies that helped control SJS and WAA. In the case of the neonicotinoids, we used the less disruptive products like Calypso and Assail that took care of key resistant pests like rosy apple aphid just before bloom or to control plum curculio at petal fall. Both products could also be used to control summer green aphids and potato leafhoppers mid-season and give additional control of codling moth and Oriental fruit moth. When the outstanding internal worm materials Delegate, Alatcor and Belt were introduced, many fruit growers went back to using the much cheaper formulations of Provado to control green aphids and potato leafhopper. While Provado could flare mites with multiple applications for apple maggot control, a single complete or two ARM applications had little if any effect on predatory mites.
Increase of Secondary Pests due to BMSB Spray Programs
As most of us know, our IPM systems were turned upside down when BMSB hit many apple growers hard starting around 2010. What about IPM in peaches, which are often hit even harder than apple by BMSB? Truthfully, the biocontrol component of IPM in peaches has been minimal for decades because of intensive pyrethroid use. Secondary pests like mites and aphids really don't cause much of a problem for peach growers, although scale damage in peach does appear to be increasing. In apple though, control of secondary pests could easily cost growers over $100/A and raise the total production costs for insecticides from the pre-BMSB level of 8% to over 25% as is being experience by many MI and NY apple growers that abandoned IPM to incorporate pyrethroids for leafroller control. Many growers surrounded by soybean and corn fields that serve as an appetizer for BMSB and without good monitoring tools to predict movement into orchards from adjacent fields or woodlots, could not afford the risk of major crop losses due to BMSB and hit them with everything but the kitchen sink. Some growers (both large and small), however, decided the risk of damage from BMSB was acceptable given their orchard layouts and surrounding landscape, but the additional cost of giving up on IPM programs and paying for additional sprays to control these secondary pests was not. Most of these growers were able to get by with border sprays of the less disruptive neonicotinoid products Venom and Scorpion (same active ingredient - Dinotefuron) to control BMSB without secondary pest problems. This ability to preserve IPM programs seems to have worked better for large growers with larger blocks and farms where damage to fruit in the border rows was only a small fraction of the total volume of apples harvested. Although still early to say for sure, BMSB populations seem to be lower this year than before. Possible explanations range from increased winter kill after the harsh winter to my favorite (of course), that native biocontrol agents including diseases are getting used to eating Chinese food. Only time will tell and it would help if we could introduce the egg parasitoids imported from China by USDA-ARS and currently under evaluation for widespread release.
For the majority of apple growers that had to give up on their IPM programs to use harsh pesticides to control BMSB, the following are some guidelines and control strategies for minimizing the impacts on mites for the next season. I will save woolly apple aphid and San Jose scale for a separate future article.
Mite flare-ups come from either the loss of predators such as T. pyri or a growth hormone-like stimulatory effect from pyrethroids and some neonicotinoid insecticdes called hormolygosis. This process can cause pest mites to have more generations in a year and more importantly with late season BMSB sprays, cause the fall mite females to lay many more overwintering mite eggs than normal. When these mite eggs hatch around bloom time the next spring, even if predatory mites have survived the sprays they can't increase fast enough to keep up with all the spider mites at petal fall to 1st cover. Trees also can't tolerate much damage at this time as the threshold is only 2.5 mites per leaf. I have seen this happen several times on farms with a good history of biological mite control after only a single spray of Endigo or Bifenthrin so that European red mite eggs reach the unheard of level of 25 mites per leaf at petal fall. Of all the products registered for BMSB control currently, the neonicotinoids are the least toxic to predatory mites (see Table 4-4 in the Pennsylvania Tree Fruit Production Guide for a complete listing of pesticide effects on T. pyri and other predatory mites). Most growers will not tolerate enough mite injury these days to get Stethorus beetles, but know that Delegate and most neonicotinoids are very toxic to our old friend which still can be very effective in processing apples on large trees where some mite injury can be tolerated. Some evidence that the neonicotinoid Belay (chlothianidin) is flaring mites the following season are under investigation, but it does not appear from last year's trials at the Penn State FREC that this is being caused by higher numbers of overwintering mite eggs like with the pyrethroids in Endigo and Leverage. We have repeated this study this fall and will be following overwintering egg numbers and continue mite counts next spring to see if mites are flaring due to a loss of predatory mites.
General Rules to Prevent Mites
- Stop using pyrethroids if possible, remember Endigo is half pyrethroid. Substitute a neonicotinoid insecticide such as Venom/Scorpion or Actara instead if possible with pre-harvest intervals. Some evidence exists that Belay (clothianidin) can flare mites in both apple and cherry when applied in the fall for BMSB, but this has not been confirmed yet.
- If a summer miticide is necessary, use a selective one such as Envidor, Nealta and Zeal as complete sprays rather than alternate row-middle. Other miticides are toxic to T. pyri and there have been resistance problems. Recent trials have shown that Agr-mek + oil at the petal fall + 7 day timing generally gives seasonal control of mites without hurting the predator mites like it used to. The disadvantage is that you have to treat generally before you know you have a problem, which is against the principle of biological control. On the other hand it is cheap and effective. It can help you to bring pest mite populations back into equilibrium with predatory mites for the next season if you have been using harsh pesticides in the past for BMSB or mitigate the effects of mites, at least if you are still using them.
Special considerations and mitigation strategies for Woolly Apple Aphid and San Jose Scale will be discussed in the next issue of Fruit Times.