by Kristen M. Castrataro
It may be mid-winter, but caterpillars were the topic of a December grower meeting held in North Scituate, RI. The event was held at Knight Farm Café and was sponsored by the University of Rhode Island’s Risk Management and Crop Insurance program.
University of Massachusetts Agricultural Risk Management Specialists Paul Russell and Tom Smiarowski provided updates on new crop insurance options and disaster relief programs available for fruit growers affected by the April 2016 freeze and the later-season drought conditions.
Due to the drought, one product of interest is a new pasture policy that uses farmer-determined rainfall thresholds to determine payments. If rainfall is below or above the thresholds for a given month, the farmer automatically receives a payment. No additional paperwork is required after the original sign-up. For growers who have found the paperwork too onerous with other crop insurance products, this is especially attractive. URI Cooperative Extension is exploring a similar product for vegetable growers as well as other options that are better-suited to New England’s unique agricultural milieu.
Following the crop insurance segment, Heather Faubert of the University of Rhode Island Cooperative Extension gave a talk entitled: “Caterpillars attacking apples and blueberries and what to do about it.”
The 2016 growing season proved how devastating high caterpillar populations could be. The combined effects of Winter Moth, Eastern Tent Caterpillars, Forest Tent Caterpillars, and Gypsy Moth Caterpillars defoliated forests, destroyed fruit crops, and mutilated Christmas tree stands across New England.
Managing caterpillars requires a knowledge of their life cycle and behavior. Winter Moth is an invasive species that entered Nova Scotia in 1930. By the 1990’s it had made its way into Massachusetts. It is now also established in Maine, Rhode Island, Connecticut, and New York. Experts expect it to continue spreading southward, but are uncertain how far west it will go.
Winter Moth is notable because the males fly around Thanksgiving and are consequently easy to identify. The females are wingless and climb tree trunks to lay eggs, making tree bands an effective way to monitor the population. Egg hatch generally begins around April 10, or when the McIntosh are at green tip. Weather heavily influences the actual hatch: this year they emerged around March 16 and continued emerging for a month.
Unsprayed apple and blueberries can have nearly 100 percent crop loss to Winter Moth, so control is imperative. A contact spray at hatch is most effective, since they are not feeding at that time. A second spray with Bacillus thuringiensis var. kurstaki (Bt-k) at tight/open cluster is recommended, as the caterpillars feed heavily then.
Researchers have been releasing a fly, Cyzenis albicans, as a biocontrol for many years. In Massachusetts, it was introduced in 41 sites. The fly is now established in 21 locations. In Rhode Island, it has been released in seven locations. Only one location has yielded results thus far. Once the parasites are established, however, they should reduce the required sprays to one per season.
Another caterpillar pest, the Eastern Tent Caterpillar, is a native. If untreated, it can become a commercial problem, particularly in apple trees. Ms. Faubert notes: “Everything loves apples and apples are host to a huge number of insects.” Fortunately, the Eastern Tent Caterpillar has natural predators that usually cause their numbers to crash. Small growers can also control them by pruning out or opening up the small eponymous tents they make.
The Forest Tent Caterpillar is another native that made its presence felt this year. Its name notwithstanding, these caterpillars do not actually make tents. Rather, they lay a silken mat where caterpillars congregate in huge masses. Forest Tent Caterpillars are usually controlled by natural predators — at least 20 types of insect feed on them.
One of the most effective predators is the Sarcophaga aldrichi. Known as the “friendly fly” for its tendency to land all over people, it is a member of the flesh fly family. The female flies deposit live maggots on caterpillar cocoons. The maggots then eat the pupae.
Despite natural predation, Forest Tent Caterpillars tend to have an outbreak every six to 16 years. Last year was such a one. They were responsible for massive defoliation, leaving only scraps for their fellow pests, the Gypsy Moth Caterpillars.
Gypsy Moths were also a significant problem in 2016. The Rhode Island Department of Environmental Management credits the Gypsy Moth with defoliating 230,000 acres of forest land out of the state’s 400,000 total acres of forest. The year before they defoliated “only” 43,000 acres in Rhode Island.
The Gypsy Moth is an invasive that entered Medford, MA in 1869. They lay egg masses containing around 500 eggs, only 20-40 percent of which are killed by egg parasitoids. The presence of 250 egg masses per acre can defoliate an orchard. The caterpillars hatch in late April or early May and can balloon into an area from nearby forests. They feed through June on anything (poison ivy, ground cover, conifers, etc.), but they prefer oaks and apples.
Biocontrol experts have tried releasing over 100 predatory insects to control Gypsy Moth Caterpillars. Two of the most successful pathogens are a virus and a fungus. Caterpillars that die as a result of the virus NPV (nucleopolyhedosis V) hang dead in a V-shape. The fungus, Entomophaga maimaiga, leaves dead caterpillars hanging upside down. The fungus was released into the landscape in 1910 and 1985. In 1989 it was found in the population.
Unfortunately, both NPV and Entomophaga maimaiga only proliferate in wet, humid conditions. May 2015 was the driest on record, and 2016 was a drought year. Those conditions provided two consecutive seasons for the Gypsy Moth population to grow nearly unabated.
What does this imply for 2017? It can be expected that the caterpillar population is going to be high and capable of considerable damage, even if the population eventually crashes. Growers of blueberries, tree fruits, and Christmas trees are advised to scout nearby woods in May for Gypsy Moth egg masses and for small black caterpillars and the threads they balloon on.
Apples and blueberries should be sprayed when Gypsy Moths are in the second instar. Near bloom, a spray of Bt can be used, but growers are advised to avoid using anything that threatens pollinators. This year it would also be prudent to spray woods abutting orchards with a Bt such as Biobit that is legal on ornamentals. A follow-up Bt spray should be used 10-14 days later to attack third instars. Once the caterpillars get larger, Bt will cease to be effective. A product such as Delegate will provide control.
As with any pest control program, Ms. Faubert stressed that scouting is paramount for achieving good control as well as minimizing spray applications. By following these steps, growers will hopefully be able to combat the expected caterpillar infestation.