Apr 15, 2016
Pest alert: green fruitworm, rosy apple aphid

We are seeing indications that numbers of green fruitworms and rosy apple aphids will be high this season. Both pests tend to flare in a cool, wet spring due to suppression of predators and other biocontrols.

Green fruitworm (Orthosia hibisci), Photo: Whitney Cranshaw/Bugwood.org
Green fruitworm (Orthosia hibisci), Photo: Whitney Cranshaw/Bugwood.org

Green Fruitworm

Last spring we saw an outbreak for the first time in many years of this sporadic pest in many parts of the state. There are some indications that numbers could be high again this year, as they are showing up in traps for other pests in high numbers at a couple of locations. Most likely the large moths are attracted to the white color of the traps or trap bottoms as they want to feed on flowers for nectar and are taking shelter from predators. The cool, wet weather we have been having this spring also seems to favor outbreaks, possibly due to suppression of biological control.

Green fruitworm is actually a complex of several species of moths that are quite common on many shade and ornamental trees, but can be a serious pest of apples and pears in Michigan, New York and New England. In Pennsylvania it is generally only a sporadic minor pest that may flare up every decade or so. In New York fruit injury at harvest may reach 10% if untreated, but normally we see very little fruit injury in Pennsylvania. Last year, this pest showed up all over the state (from York to Bedford) in much higher numbers than ever seen before. Normally, pink or petal fall sprays would take out this pest, but newer products like Calypso, Assail, Sivanto, and Avaunt have little effect on the larvae. Although reported to be somewhat tolerant to OP insecticides, Guthion probably gave some control in the past but lower rates of Imidan have been ineffective. Some mortality from thinning from Sevin (carbaryl) also has been seen, but only at rates of at least 1 qt/100 gal or higher and not enough to ensure control.

Control

Our recommendation if you need to control this pest is 8-12 fl oz/A of Intrepid at pink, which is very safe to all beneficial insects including bees and has long residual activity on foliage. This application timing will also give excellent control any gypsy moth larvae that might blow in from adjacent wooded areas.

Delegate, Altacor and Belt would also be effective, but are more expensive and you would want to save the limited number of applications of this product for codling moth control at the approximately 1st and 2nd cover timings.

Intrepid sprays at this time would also help supplement codling moth control as it works as an ovicide for that pest and it has long residual control of any redbanded, tufted apple bud moth, and obliquebanded leafrollers that might also be present. OBLR, is harder to control and a 12-16 fl oz/A rate is necessary to control them if pressure is high.

Bt products such as Dipel are also sometime recommended for organic production, but are generally less effective, especially on larger larvae. Intrepid will kill even the larger larvae we would see in the next couple of weeks , but the rate should be increased to at least 12 fl oz/A. We have seen tank mixes of Intrepid and Bt products result in quicker kills of the larger larvae over either product alone.

How to recognize this pest

The larvae we have seen so far have all been of the Speckled Green Fruitworm (Orthosia hibisci) early instars which are only about 1Ž4 to 1Ž2 inch long currently and have a green head capsule and light green body with white stripes that are more pronounced in the larger larvae. You many need a hand lens to see these stripes and while the light green form is most common, there are also darker forms (Fig.1).

Figure 1. Note the stripes on both the light green form and the darker form of larvae.
Figure 1. Note the stripes on both the light green form and the darker form of larvae. Photos: Penn State Extension

Smaller larvae look very similar to redbanded leafroller larvae and use webbing to fold young leaves into shelters in a similar way and you may first notice these shelters and the small feeding holes in leaves. Full grown larvae get rather large (1.5 inches and will feed on developing fruit until they reach 1inch in diameter at which time they move to the ground and pupate in the soil. (end of May to early June). Green fruitworms fortunately have only a single generation, so this pupae will stay in the ground all summer and overwinter to emerge early in the spring with each female moth laying several hundred eggs at the 1Ž2 inch green stage. Adults are relatively large brown moths (over 1Ž2 inch long) which are quite ‘fuzzy’ in appearance with darker brown square spots on the forewings (Fig. 2).

Feeding by small larvae from the pink through bloom period is not serious and results mostly in some blossom thinning and a little foliar injury. It is the bigger larvae feeding on small developing fruit that cause the economic injury. Damage to the larger fruit in the next couple of weeks will result in deeply scarred and russetted fruit which are unsaleable. Damage to pear fruit appears to be less likely to abort and be present at harvest. A single larvae will feed on as many as a dozen fruit, of which at least 70% will abort.

Figure 2. Adult green fruitworm moths
Figure 2. Adult green fruitworm moths.

Monitoring

While there is a pheromone for the green fruitworm, it is generally not the best way to monitor for this pest since it has so many alternate hosts, flies long distances, and is such a sporadic pest in our region. The best way to tell if you have a problem is to examine the growing shoots and leaves from several trees in your blocks starting at petal fall for the shelters and feeding. While no spray thresholds have been set, the presence of several larvae on most trees would warrant a spray. Biological control in natural areas keeps populations down and keep populations low in most seasons, but are not effective enough in orchards to stop occasional outbreaks.

Rosy apple aphid

Rosy apple aphid also flare in a cool, wet spring as we are experiencing due to suppression of predators and other biocontrol. We have seen resistance in this pest to Lorsban and pyrethroids for over a decade in most orchards in the state and have shifted to the use of plant systemic neonicotinoids for controlling this pest. Applications made at petal fall are ‘revenge’ sprays which will eliminate the colonies, but only after they have caused about 80% of the injury during bloom that stunts the fruit growth. Likewise, biological control can eventually eliminate this pest post-bloom, but again only after the fruit stunting has occurred (Fig. 3).

Figure 3. Rosy apple aphid damage
Figure 3. Rosy apple aphid damage.

Because of issues with pesticides and pollinators, we do not recommend any insecticides, except possibly Bt and Intrepid during bloom. Neoniciotinoid insecticides are, of course, of special concern with pollinators because they are plant systemic and can move into the nectar and pollen from pre-bloom sprays. The old precaution of ‘only spray when the bees are not present (early morning or at night)’ has little meaning for these product and other plant systemic products since contact exposure is not an issue unless you are spraying during bloom (not legal with most products and not recommended with Assail). Although the levels we have found in our research (10-40 ppb from the pink stage application), are considered to be safe by EPA honey bee measures, we have taken the IPM stance of using only the most bee safe neonicotinoids (Assail, Calypso, and Sivanto) and only at the safest timings (Figs. 4 & 5). We want to control RAA but minimize residues to honey bees and wild bees from contaminated pollen and nectar. This timing with maximum efficacy on RAA and minimal pesticide residues in the pollen and nectar at bloom has been the 1Ž2 in green stage.

Figure 4
Figure 4.
Figure 5.
Figure 5.

Unfortunately, that timing has passed for many growers due to the poor weather and many growers will be trying to control this pest at pink or even king bloom this season. As can be seen in previous tables, while the new product, Sivanto, is very safe to bees by contact (sprayed directly on the bee flying in the orchard or from residues on the flower petals), but more toxic than Calypso or Assail by ingestion of the pollen and nectar that has been contaminated through the systemic movement of the pesticide through the plant from a pre-bloom spray and into these tissues. Spraying during bloom would not only raise these levels in the pollen and nectar, but would also add contact poisoning as a mortality factor.

Since Calypso was withdrawn from the market to make room for the Sivanto registration, most growers have used up existing stocks of that product which really only leaves Assail as the neonicotinoid of choice for a pink or slightly later application for RAA control that should minimally impact pollinators. We normally recommend the Assail rate at 6 oz/A at pink for RAA control, but many growers are using a lower rate of 3.2-4 oz/A which I would be concerned about under high RAA pressure.

Another option we have been researching over the last couple of years in case blanket bans of neonicotinoids occurs as they have done in Europe and as a resistance management rotation with neonicotinoids has been Beleaf (flonicamid). Invariably, when I mention this product to growers they confuse it with Belay (clothianidin) which is the most bee toxic neonicotinoid insecticide. Belay is labeled for post-bloom use and some growers use it for Brown Marmorated Stink Bug control in the fall.

Beleaf is not a neonicotinoid and is very safe to bees both by contact and ingestion according to our current information (Figs. 4 & 5). It has a unique mode of action that works by paralyzing the mouthparts of sucking insects such as aphids and leafhoppers with little effect on other insects, although we are evaluating it for codling moth control this season. Beleaf is plant systemic and shows up in the pollen at levels of up to 500 ppb from pre-bloom sprays, but has not been found in the nectar. This level of Beleaf is currently considered to be safe to bees, but we will be investigating the effects of wild bee larvae feeding on contaminated pollen soon. The efficacy of Beleaf in controlling RAA has been just as good with the neonicotinoids in our trials under high pressure and we feel it is another relatively bee safe product that could be used at this pink timing. The rate for Beleaf is 2.8 oz/A which is comparable in cost to the lowest rates of Assail.

— Grzegorz Krawcyzk and Dave Biddinger, Penn State University

Source: Penn State Extension





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