Left: Rosy apple aphid and damage. Right: White apple leafhopper and damage.
Evaluating Pesticide Impact on Beneficials
This means evaluating the pesticide impact not only on the target pest, but also the beneficial organisms in the orchard. For example, both the spotted tentiform leafminer and the white apple leafhopper were important pests of apple in Pennsylvania. They were difficult to control as only a few products like Lannate, Cygon, Carzol, and Vydate were effective on them, but these pesticides were devastating to biological control agents that helped keep the pests' populations low. With the introduction of the neonicotinoid insecticide Provado (imidacloprid) in the late 1990s (and subsequently Confirm and Spintor), leafhopper and leafminer populations declined to the point where they are no longer important pests. In addition, these new pesticides were not as harsh on beneficials, allowing more predators and parasitoids to enter the orchard and give the grower a hand in pest management.
Neonics Changed IPM Programs - generally for the better
Despite the bad press they have been receiving lately due to possible impacts on bees, the neonic class of insecticides greatly changed our IPM programs, and generally for the better, as they replaced more toxic organophosphate compounds. When rosy apple aphid began to develop resistance to Lorsban and pyrethroids around the turn of the century, it was neonic products like Assail and Calypso that brought this important pest back under control. While these products were probably largely responsible for the decline of Stethorus as a mite predator, it was quickly replaced with the phytoseiid predatory mite, Typhlodromus pyri, which is resistant to the neonics and a much more effective mite predator. It was the previous heavy use of Lannate for resistant leafroller and for leafminer and leafhopper control that probably prevented the predatory mites from becoming effective prior to this and why the highly mobile (flying) Stethorus could move rapidly to developing mite outbreaks. While direct contact of neonicotinoids sprays are toxic to many beneficial predators and parasites, the quick absorption of these products into the leaf tissue, and subsequent systemic movement throughout the plant, protects most non-plant feeding insects and mites. In addition, the neonics are much safer to the consumer and orchard workers than the products they replaced when the Food Quality Protection Act forced many of the more toxic pesticides from the orchard. While multiple applications of high rates of some neonics can cause flare-ups of some secondary pests like mites and woolly apple aphids, the limited use of these products has reduced outbreaks of secondary pests and has increased biological control over the Guthion+Lannate based programs they replaced.
From about 1999 to 2005, our key pests of apple orchards transitioned from leafrollers like tufted apple budmoth to internal fruit feeders like Oriental fruit moth (OFM) and codling moth (CM). While the insect growth regulators (IGRs) Confirm and Intrepid were fantastic in controlling leafrollers, they were not very effective on OFM and could not hold up to high pressure populations of CM. For a couple of years we shifted to another type of IGR called Rimon, which was more effective on the internal worms and leafminers, but was somewhat less effective on leafrollers, and tended to flare mites and wooly apple aphids by killing off some types of predators. Around 2006, the neonicotinoid Assail was registered on apple and as it proved more effective on internal worms, it quickly replaced Rimon. Another neonicotinoid, Calypso, was registered the following year and although slightly less effective on internal worms than Assail, it proved to be as good as Guthion for plum curculio and apple maggot control. Both products were of course, also very effective on sucking insects and the timing of sprays to control internal worms also greatly reduced our summer green aphids, leafhoppers and leafminers. The exception has been the woolly apple aphid, which has not been effectively controlled by the neonics. A couple of years later, around 2008 to 2009, Delegate and Altacor were registered in apple and again changed our IPM programs as they were much better in controlling internal worms and replace the majority of the neonic sprays that were timed for codling moth. Like Spintor, the related compound Delegate also inadvertently helps control leafminer and leafhopper populations when used for internal worm control. Alatcor and the related compounds Belt and Tourismo also have long residual control on leafminers, which is probably why we can't find any in commercial orchards anymore.
So How do the Neonics Fit into our Current IPM Programs?
Striking the IPM balance involves controlling the pest, reducing harm to beneficials and protecting pollinators. All of these factors should be considered when choosing any pesticide. In an attempt to minimize the use of neonics in our apple IPM programs, the following 3 uses of neonics are ranked in terms of importance and lack of IPM friendly alternatives.
1) Rosy Apple Aphid (RAA)
The most important remaining use for neonics in apple is for the control of Lorsban and pyrethroid resistant RAA which is prevalent in most Pennsylvania orchards. RAA can cause serious stunting of tree and fruit growth. Unfortunately, biological control agents are mostly ineffective partially because the economic threshold for this pest is very low at only a single colony/tree on average.
What is the optimal timing for RAA control?
Between ¼ inch green and pink is the best timing for this pest. Only a single application is necessary. While we have recommended the pre-pink to pink timing as being most effective in the past, our investigations into bee toxicity have shown significant movement of neonicotinoids into the pollen and nectar at apple bloom from a pink application made 5 days previously. We are currently investigating whether earlier applications can give equivalent levels of RAA control, but minimize movement into the pollen and nectar.
Which products to use for RAA?
Only Calypso or Assail are recommended currently as they are safer to bees by at least 200X than the other neonic products. Provado is not labeled for use pre-bloom because of the bee issue, but Actara and Belay are allowed despite being even more bee toxic than Provado. Be aware that while the Assail label allows for use during bloom, we do not recommend this because of bee issues not only from contact (but I sprayed at night!), but because of the systemic movement directly into the pollen and nectar from the open flower.
Rosy apple aphid is relatively easy to control compared to internal worms, so a 4 fl oz/A rate of Calypso or a 6 oz rate of Assail are recommended. Calypso was the most bee safe neonic; however, the recent voluntary withdrawal of the registration means that only existing stocks can be used. The loss of this insecticide from the market will leave a large void in available options for controlling plum curculio and apple maggot. Other closely related products such as Closer and Nealta are being evaluated for RAA control and impacts on bees and look promising, but are not direct replacements for Calypso.
Can't I wait until petal fall to use Provado to clean up RAA?
Definitely not! This is what Larry Hull and I used to call a 'revenge spray' since you will kill the aphids, but only after about 80% of the shoot injury and fruit stunting has occurred.
2) Potato Leafhopper (PLH)
This pest does not overwinter in our area, but moves up from the South each year on warm air masses from storms. While PLH is generally more of a problem in areas with lots of field and forage crops, it can move like a cloud from cut alfalfa into an orchard overnight. Young, nonbearing trees are most affected by both PLH and RAA, but severe PLH can completely stop the growth of young trees and contribute towards death of the trees under stress such as from drought. PLH has also been implicated in the movement of fire blight between orchards. PLH feeds on tender young terminal leaves and initial feeding turns the leaves yellow around the edges. These leaves quickly become chlorotic and deformed so that the leaves are cupped upward and then turn brown and scorched into what we call 'hopper burn.' The damage is caused by a plant's adverse reaction to the PLH saliva and is often mistaken for injury by herbicides or nutrient deficiency. The most effective and cheapest control is provided by the neonics of which all appear to be equally effective, but the more systemic Provado, Actara, and Clutch give the longest residual activity. In our area, unless you are next to a hay field (which is most attractive to PLH) that is periodically being mowed, a single application of Provado at a low 2-4 fl oz rate/A has been effective. In a drought year, multiple applications may be necessary as weeds and other hosts dry up. For other neonic products the low-end rates are generally effective.
Since movement to apple can be very rapid from other host, many prefer to put on a preventative spray just as cherries begin to develop some color (about now this season, but usually just before the 4th of July weekend. For those that take the time to monitor, the threshold is an average of one nymph/leaf. You can count the adults as well, but generally they fly when disturbed.
3) Brown Marmorated Stink Bug (BMSB)
Actara and Scorpion/Venom (dinotefuran) are effective in controlling this pest and the least disruptive control options currently available to the biological control of secondary pests like mites, woolly apple aphid and San Jose scale. Dinotefuran containing products have a short 3 day pre-harvest interval for late season use on peach and nectarine and have again received a Section 18 Emergency registration for use on BMSB in apple and pear.