April 16, 2008
In this Issue:
What to Look for/Do Now:
Insect and Disease Activity
The speckled green fruitworm is the most common of the green fruitworms that occur in Utah and adult moths are emerging now. They are stout, and reddish-brown in color. It overwintered as a pupa in the soil and typically emerges in March to April to mate and lay eggs on both pome and stone fruit trees, as well as several ornamental species. It can lay up to 300 eggs in one large cluster. The eggs begin hatching during apple bloom or cherry petal fall.
The young larvae feed on flowers and leaves while the older larvae can also feed on fruit (see above). Damaged fruit can drop early or show deep sunken areas. Injury looks similar to leafroller feeding, but is deeper. There is just one generation per year.
Treatment: Treatments used for other pests (codling moth, peach twig borer, etc.) will also take care of fruitworms. Otherwise, use Bt (Foray, Dipel, etc.) or spinosad (Entrust, Success) at bloom during dawn or dusk.
Both of these aphids are beginning egg hatch now, but the green apple aphid (the most common aphid of apples) won’t increase significantly until the warmer summer months. The rosy apple aphid is more of a problem in spring. They inject a toxic saliva during feeding, causing curled leaves and stunted and deformed fruits (as shown above). They migrate out of the apple orchard to weed hosts in late June and July. Green apple aphids remain in the orchard for the entire season.
Treatment: Delayed dormant (up to 1/2” green) oil (or oil plus Lorsban) will kill most overwintering eggs and emerging nymphs.
Peach twig borers spend the winter as a small larvae in galleries (hibernacula, shown below) within the tree cambium. They emerge as leaves begin expanding to seek the first flush of new growth. There they bore into the tip of shoots, causing the typical “shoot strikes.” Later generations feed on the fruit.
Treatment: A pre-bloom application has been an effective means of controlling the overwintering larvae as they begin to stir. This is a good time for control as it is made before bees and other pollinators are active. Materials: oil plus esfenvalerate (Asana for commercial; Ortho Bug-B-Gon or Ortho Max for residential), spinosad, malathion, sevin.
If twig borer was not a significant problem last year, then a pair of bloom-time applications of Bt at dusk (early bloom, and again at post bloom) are very selective, highly effective, and harmless to pollinators.
Some commercial growers also use mating disruption to help suppress peach twig borer, and is often used in conjunction with the delayed dormant and bloom-time applications. It is most effective in orchards with low pest pressure, and in sites that are not adjacent to uncontrolled peaches. Dispensers are hung at or just before biofix, or at 400-450 degree days (base 50) after March 1.
Degree Day Accumulations (March 1 - April 15)
The use of insect pheromones in orchards allows us not only to monitor for insect pests, but to manage them, as well. Pheromones are chemicals that insects use to communicate with one another, and our interest is in the pheromones (of mostly moth species) that are released by females to attract males for mating. These species-specific chemicals are synthesized and imbedded in a rubber lure to use on sticky traps to determine the presence and abundance of certain moth pests. But when dispersed in large quantities over great distances, pheromones can also be useful in suppressing pest damage by preventing mating. For the last 10 years, mating disruption (MD) has been a valuable tool for commercial apple and pear growers in suppressing codling moth damage.
Notice that “commercial growers” is written above. That is because the use of mating disruption only works in orchards 10 acres in size or more, and the typical residential orchard is much smaller. Mating disruption will not work on smaller orchards because it does not prevent mated females from neighboring locations from flying into the orchard.
How it Works
In a non-treated environment, the plume of “scent” that a female releases can be detected hundreds of yards away by males, and “hangs” in the air in such a way that the male can follow the scent through the plume, almost always zeroing in on the female. When enough artificial sources of pheromones saturate the air, the probability of males finding females is significantly reduced. They are unable to follow one specific plume, and wander for days. When no mating occurs, injury to fruits is also reduced.
There are four theories presented by Michigan State University researchers of how males are prevented from finding females:
The competition theory holds the most weight in explaining how MD works. The mating of males and females may not be completely disrupted, but is significantly delayed. Eventually, some males will find females. But by the time they meet (a delay of 2-3 days) the fecundity of the females is reduced by more than 50%.
Using Mating Disruption
Mating disruption programs should be considered as one tactic within the toolbox of pest management options. In any orchard where there was codling moth injury in the past, supplemental cover sprays will be necessary. You may wonder, “if I have to spray anyway, why pay for the mating disruption?” It is a proven-effective component of an IPM program because, over time, it significantly reduces the overall target insect population. (Getting all neighboring orchards of suitable size will speed this process along.) Eventually, the number of sprays will be significantly reduced. It is highly selective, and there are virtually no mammalian or environmental health risks.
The commercially available MD dispensers that are most commonly in use are placed in the orchard in a high number of points (200-400) per acre. To prevent all mating, they should be hung in the orchard before biofix. (Although it is imperative that growers get a biofix from a comparable, non-MD location to time supplemental sprays.) These hand-applied dispensers should be placed as high as possible in each tree.
The standard brands (Isomate, Checkmate) utilize wires, clips, or circular twin tubes and are twist-tied or clipped directly onto branches. These products last approximately 120 days, allowing for pest suppression for most of the growing season. Isomate CTT (Pacific Biocontrol) is a more concentrated formulation and is applied at 200 points/acres.
Results of Mating Disruption Studies at Washington State University
Monitoring in a MD Orchard
Growers should continue to monitor for codling moth during the season to evaluate the effectiveness of the mating disruption, and to determine if supplemental sprays are needed. Two types of lures, a “megalure” (also called 10x) releases more pheromone than the typical lure so that it is still attractive to males. Another lure called the DA-combo is a combination of the megalure and a synthetic pear ester. The pear ester is easily distinguished from the pheromone by males and females, and both sexes are attracted to this lure. Although research on action thresholds in Utah is ongoing, we currently recommend treatment when 5 moths have been caught with either type of lure.
For dormant and delayed-dormant timing
Note that these treatments are only recommended if you know you have the particular pest in your trees.
Precautionary Statement: All pesticides have benefits and risks, however following the label will maximize the benefits and reduce risks. Pay attention to the directions for use and follow precautionary statements. Pesticide labels are considered legal documents containing instructions and limitations. Inconsistent use of the product or disregarding the label is a violation of both federal and state laws. The pesticide applicator is legally responsible for proper use. Any mention of a pesticide brand in this document is not an endorsement by USU, and brand lists are not all-inclusive.