May 10, 2004 Volume 13 No. 8 Update on Pest Management and Crop Development
Highland: Plum Curculio caught in trunk trap.
Mullein Plant Bug
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
White Apple Leafhopper
Mullein Plant Bug
Oriental Fruit Moth
San Jose Scale
Spotted Tentiform Leafminer
White Apple Leafhopper
[Editors' note: To whet your appetite for impending confrontations with the 2nd generation oriental fruit moth in apples, which might be expected in early to mid-July, we thought we'd reprint the following synopsis of some small-plot insecticide efficacy trials conducted last season.]
These treatments were tested in small plots set up in two commercial orchards in western NY that had been severely infested with internal Lepidoptera during the previous (2002) growing season. Trees in the test plots received normal applications of fungicides, but were not treated with any insecticides early in the season to allow pressure from the early generations of Lepidoptera to build up in the research plots. Treatments were applied by a hand gun sprayer on 16 and 29 July against the estimated activity of the second brood of OFM, and again on 14 and 27 August against the third brood of this pest.
The initial sprays for each generation were timed to coincide with the estimated first hatch of eggs of OFM (175-200 DD base 50°F) after pheromone trap catches indicated the beginning of the second and third flights of OFM. Treatments were replicated 4 times at the first location and 3 times at the second location on single-tree plots separated by unsprayed buffer trees and arranged in a RCB design. 'Ida Red' apples were treated at the first site and the second site was a mixed planting of 'Ida Red' and 'Twenty-Ounce'. Fruit damage was initially estimated by randomly picking 100 apples per treatment in each rep at both locations on 14 September, which was about 14 days after the last treatments were applied and again on 10 October, which was a normal harvest date for these cultivars. Damage was compared in these two samples to determine if any late season damage had occurred after the residual effects of the pesticides had diminished.
Damage was assessed as either "deep" (internal trail greater than 1/16") or "sting" (internal trail less than 1/16"). Internal Lepidoptera populations built up to high levels in both sites as indicated by the high levels of damage found in the untreated check plots. The organophosphate treatments (Guthion & Imidan) were statistically as effective as Calypso, Assail, Diamond, Warrior, Avaunt and Intrepid, although damage in the Avaunt and Intrepid plots was the highest among this group of compounds. Esteem and Deliver did not adequately protect fruit. Assail was the most effective treatment at both locations in protecting fruit at harvest, followed by Warrior and Diamond. The two standard organophosphates, Imidan and Guthion, were similar in effectiveness and these treatments were statistically as effective as any of the other compounds except Assail. Therefore, it appears that organophosphates can still be used to control internal Lepidoptera in most NY apple orchards, even though preliminary studies have suggested that some field populations of OFM have low levels of resistance to these materials. Damage in the later samples harvested on October 10 was higher than that observed on September 14 in all treatments, except Assail. These results show that most compounds applied during late August cannot provide adequate residual protection of fruit during September and October in apple orchards in which pressure from internal Lepidoptera is extremely high.
Means within a column followed by the same letter are not significantly different (Fisher's Protected LSD Test, P<0.05). Data transformed Arcsin (Sqrt X) prior to analysis.
MANAGING BLOSSOM BLIGHT
Inoculum produced from infected blossoms is further spread by wind, rain, and insects. Shoot tip infections are likely to occur when shoots are actively growing and daily temperatures average 60°F (16°C) or more. In years when blossom infections do not occur, the primary sources of inoculum for the shoot blight phase are the overwintering cankers, particularly young water sprouts near these cankers that become infected as the bacteria move into them systemically from the canker margins. In the absence of blossom infections, the development of shoot blight infections is often localized around areas with overwintering cankers.
Rootstock blight is associated primarily with the highly susceptible rootstocks such as M.26 and M.9. On these trees, just a few blossom or shoot infections on the scion cultivar can supply bacteria that move systemically into the rootstock where a canker may develop and girdle the tree. Trees affected by rootstock blight generally show symptoms of decline and early death by mid- to late season. Sometimes symptoms may not be apparent until the following spring.
Although mature shoot and limb tissues are generally resistant to infection by E. amylovora, injuries caused by hail, late frosts of 28°F (-2°C) or lower, and high winds that damage the foliage breach the normal defense mechanisms in mature tissues. Instances of fire blight that originate with infections at sites of injury is called trauma blight and may affect even normally resistant cultivars like 'Delicious'.
Disease management during bloom
Streptomycin: Streptomycin applications during bloom are highly effective against the blossom blight phase of the disease. These sprays are critical because effective early season control often prevents the disease from becoming established in an orchard. Predictive models, particularly MARYBLYT and Cougar Blight, help to identify potential infection periods and improve the timing of streptomycin, as well as avoid unnecessary treatments, particularly during the blossom blight phase of the epidemic. Streptomycin applications are best used in a preventive mode, just prior to an infection event. You can expect at least 3 days of protection from streptomycin applied to open blossoms. In trials conducted by Keith Yoder in Virginia, approximately 50% reduction in fire blight was achieved on unopened blossoms sprayed with streptomycin that were inoculated with fire blight after they opened the following day. Higher levels of control are likely with lower inoculum levels, but excellent spray coverage is critical for protecting flowers. If you miss an infection event, it is critical that streptomycin be applied within 24 hours to reduce blossom blight. Using predictive models (e.g., MARYBLYT), it is possible to use local weather forecasts to predict whether an infection event is likely to occur in the next day or two. This can be extremely helpful in identifying unusually high-risk situations. In younger orchards, removing blossoms by hand will reduce the risk of blossom infection. This practice can be especially effective in minimizing losses due to rootstock blight as well, particularly when highly susceptible varieties such as 'Gala' or 'Gingergold' are grafted on to M.9 or M.26. Although somewhat time consuming, blossom removal is a much less expensive alternative than replanting an entire block.
Trauma events (hail, high winds) can put any orchard block at risk because varieties that are considered relatively resistant to blossom blight and shoot blight can suffer severe blight under trauma conditions. If a trauma event occurs when trees are actively growing, application of streptomycin within 12-24 hours after the trauma event may limit the severity of the resultant trauma blight. After midsummer when trees have hardened off for the season, streptomycin protection following trauma events may be unnecessary because trees are thought to be fairly resistant to fire blight after tree growth stops for the season. Applications of streptomycin may be not be possible after midsummer anyway because of the days-to-harvest limitations on the label.
Serenade is a biofungicide labeled for control of fire blight. Serenade is a wettable powder formulation of the bacterium Bacillus subtilis (strain QST713), a common soil resident. The bacterium acts by releasing cell contents during growth in order to eliminate or reduce competitors in its immediate environment. In limited testing in New York, it has shown fair activity against fire blight when used in alternation with streptomycin. Serenade should be applied as a preventive and can be applied up to and including the day of harvest. Serenade has been promoted as a tool for managing streptomycin resistance, but its effectiveness for resistance management remains unproven. If you choose to use Serenade, we (i.e., Cornell pathologists) strongly encourage that it be used in a rotational program with streptomycin and not as the sole bactericide for fire blight management. Research at Geneva suggests that streptomycin should be the first product applied during bloom, particularly when conditions are very favorable for the development of fire blight.
Timing streptomycin sprays according to MARYBLYT
MARYBLYT integrates 3 cumulative heat unit "clocks" to indirectly monitor host (flowering), pathogen (epiphytic inoculum potential [or EIP]), and symptom development. The "clocks" calculate either degree days or degree hours under a given temperature base. MB uses the following four criteria to predict blossom blight:
When all 4 conditions are met in the sequence given, infection occurs. The first symptoms appear with the subsequent accumulation of 103 degree days greater than 55°F. In real time, this interval can vary between 5 to 30 or more days. The degree to which any of the thresholds exceed their minimums provides a subjective basis for estimating the severity of blossom blight infection. Cool weather has a negative effect on EIP. Specifically, a 3-day cool period (i.e., no temperature greater than 65°F) reduces EIP to 0 unless EIP had previously exceeded 200. The first cool day reduces the EIP by a third, the second by a half, and the last sets the EIP to 0. Also, the EIP is reset to zero after an antibiotic application under the assumption that this spray reduced bacterial populations to marginal levels.
MARYBLYT uses a simple +/- system to score whether or not the threshold of any of the 4 criteria have been met. Risk of infection is then rated as 'low', 'moderate', 'high', or 'infection' depending upon whether one, two, three or all four of the thresholds have been exceeded, respectively. Although infection is predicted only when all four thresholds are exceeded, infections can occur in less favorable conditions, i.e., when only 2 or 3 thresholds are exceeded. In practice, any combination of those 4 thresholds could be used as a rule to trigger a management action. Our current evaluation of MARYBLYT has shown that timing applications only when all 4 parameters have been "triggered" results in the fewest OVERALL mistakes. That is, a balance between 1) spraying UNECESSARILY, and 2) missing a NECESSARY spray. Because the latter mistake is potentially more costly than the former, particularly on susceptible varieties, a simple set of guidelines on how to best use MB was devised. The guidelines are 1) Moderately susceptible varieties should be sprayed only when MARYBLYT rates the risk "infection" (all 4 parameters exceeded); 2) Susceptible varieties should receive an application when MARYBLYT rates the risk "infection" -- a conservative approach would also suggest an application when MARYBLYT rates the risk as "high" (any three parameters exceeded); 3) Young trees should be sprayed when MARYBLYT rates the risk as "high" or "infection" (all 4 parameters exceeded).