April 29, 2002 Volume 11 No. 7 Update on Pest Management and Crop Development
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TRAP CATCHES (Number/trap/day)
Geneva: No Activity!
(Bill Turechek, Plant Pathology, Geneva)
Fire blight is one of the few diseases that can completely destroy an apple crop in a single infection event. The record warm temperatures that pushed many apple varieties into bloom in the Hudson Valley nearly two weeks ago (April 15-19) was followed by heavy rains that almost certainly resulted in significant fire blight infection, particularly if trees were left unprotected. This event was followed by a hard frost on April 23 that left many in the industry wondering what further damage was done and, more importantly, what could be done about it.
In an early morning meeting on April 24th, Dave Rosenberger, Mike Fargione, and Jim Schupp examined the situation, the potential for heavy losses, and management alternatives. They drafted a letter outlining management options and mailed it to Hudson Valley growers by week's end. An excerpt from this letter is printed below. The recommendations outlined in this letter ARE NOT directed to growers in western New York as we did not experience the same series of events as Hudson Valley growers. Rather, this letter presents a scenario and possible solutions that, although unlikely, could occur in western New York. There will undoubtedly be disagreement about the role frost injury plays in fire blight epidemics. However, given the lack of scientific data, it is best to err on the side of caution given the proximity of the injury to a significant infection event:
The Pessimist's Perspective - Reasons for believing that fire blight will decimate Hudson Valley orchards in 2002:
1. Hot weather during bloom favored severe blight: The MARYBLYT computer model showed that we had 3.7 times as much heat as would be required for a blight infection. When temperatures get into the 80's during bloom, blight becomes very difficult to control and outbreaks often include cultivars such as 'Delicious' that are normally not very susceptible to fire blight.
2. Dews on Wednesday and Thursday mornings (April 17 & 18) may have been sufficient to trigger infections. We do not have good data on how often dews trigger infections or on how to measure dew periods. However, infection from dews has been reported in the scientific literature. Not many apple blossoms were open on Wednesday AM, but the dew on Thursday AM might have triggered infections in many apple orchards.
3. Streptomycin applied on Saturday AM after the Friday rains may not provide 100% control. Streptomycin provides reasonable control of blight when applied within 24 hours after infection under moderate disease pressure, but the after-infection activity is not quite as good as the protectant effect of applying streptomycin ahead of rains. Streptomycin applied on Saturday AM would have been more than 24 hours after any dew-related infections on Thursday AM and may not have provided complete control of Friday afternoon infections where inoculum levels were very high.
4. The frost on Wednesday AM (April 24) may have made matters worse. Many fire blight researchers discount the relevance of frost events. However, Rosenberger believes (based on 45 observed epidemics) that frost following infection events may increase the severity of blight epidemics by enabling sub-lethal concentrations of bacteria to initiate disease in the frost-damaged tissue. Where streptomycin sprays were applied on April 19 (and perhaps where orchards were sprayed on April 20), the frost should have no effect on disease development because the bacteria were killed prior to the freeze event. Where no streptomycin was applied, however, the frost could turn a bad situation into a disaster.
The pessimistic conclusion: Fire blight will be severe, extensive, and will affect even cultivars that are only moderately susceptible to blight. Apply Apogee to any blocks that could possibly be considered at risk for fire blight, including blocks where streptomycin application was delayed until Saturday morning, and including cultivars such as 'Delicious' that are considered only moderately susceptible to blight. [Bill's note: Blocks "at risk" would mean any block that has had fire blight in the past two years.]
The Optimist's Perspective - Reasons for believing that blight will not be very severe:
1. It was too hot for severe blight: Temperatures in the 80's are ideal for blight, but some research suggests that temperatures >90°F decreases blight risk. High temperatures recorded at the Hudson Valley Lab for Monday through Friday (April 15-19) were 81, 88, 94, 91, and 85°F.
2. Humidity was too low: The greatest risks occur when temperatures in the 80's are combined with high relative humidity (>70-80%). We did not have high relative humidity prior to Friday morning except for a few hours on Wednesday and Thursday mornings.
3. There was no wind during the hot days to aid in spreading the blight bacteria or to cause wind-whip injuries where infections could occur.
4. It got too cold following the Friday rain: The worst blight occurs when ideal temperatures (mean daily temp >60°F) persist for a few days following an infection event. Our mean temperatures for Saturday and Sunday stayed below 60°F.
5. The frost was irrelevant: There is no solid data to implicate frosts, especially when several days of cold weather occur between the last warm day and the timing of the frost.
6. Few bees were present to spread the blight: Most people did not have bee hives in the orchards because of the rapid onset of bloom, so the spread of blight may have been less efficient that it would have been had the bees been in place.
The optimistic conclusion: Anyone who sprayed streptomycin on Friday or Saturday last week (April 1920) has nothing to worry about. Apogee should be considered for high-risk blocks that did not get any
Streptomycin last week.
Growers in the Hudson Valley should have taken this information into consideration when making pesticide applications last weekend. Within the next few weeks, we will be able to better ascertain what the "correct" action was and whether or not Apogee was needed.
Apogee (Prohexadione Calcium) is a relatively new product for managing shoot blight infections. Apogee is a growth regulator and works by "shutting down" the growth of a tree and, therefore, is used primarily to control overly vigorous trees and reduce the need for seasonal pruning (see the articles written by Jim Schupp in the first two issues of Scaffolds). Apogee has value in fire blight management because when trees stop growing, they become relatively resistant to new blight infections and further expansion of established infections is arrested. Thus, Apogee can significantly reduce secondary spread of fire blight (i.e., shoot blight infections) in orchards where streptomycin sprays failed to provide 100% control of blossom blight. Apogee has no effect on shoot growth or fire blight for at least 10 days after application, so it acts too slowly to be of value as a rescue treatment for orchards with blight symptoms. Apogee is ineffective for control of the blossom blight phase of the disease and is registered only for apples, not for pears.
In mature orchards where trees have already filled their spaces, the decision whether or not to use Apogee can be based on a combination of its potential value as a vegetative growth inhibitor and as a supplement to fire blight control. In young orchards where trees have not yet filled their spaces, the decision is much more complex. Using Apogee for fire blight control in young orchards will reduce vegetative growth. That, in turn, will decrease profitability of the orchard in succeeding years because it will increase the number of years required for trees to fill their spaces and for the orchard to reach the break-even point. Because of this, growers need to seriously consider whether the delay to reaching full production or the reduction in fruiting capacity outweighs the potential loss due to fire blight. But one thing is certain, the cost of using Apogee is certainly cheaper than
ANOTHER ORGANIC EXPERIENCE
The past few years have brought about ground-shaking changes in pesticide uses and legislation. In an effort to roll with these changes, research has been conducted both here at the Geneva Station and in private orchards to test the efficacy of not only the new generation of currently available conventional insecticides, but some of the organic options as well. In the 2000 growing season, handgun applications of several materials were made in orchards at Geneva on a season-long basis. The results of this project was discussed last spring in Scaffolds, and (in case you can't find your back issues) are currently available online at http://www.nysaes.cornell.edu/ent/scaffolds/2001/4.2_insects.html. The 2001 growing season saw another project with organic materials with a slightly different twist.
With the cooperation of a western NY grower who agreed to apply the materials, a field project was conducted using an airblast sprayer in an already certified organic orchard. The block of approximately 10 acres of 'Delicious' and "Cortland' trees was evenly split into two treatments. Surround, the particle film formulation of kaolin, was applied from petal fall on a weekly schedule until the final cover spray in mid-August in half of the block, while the other half received Surround at petal fall, and then again weekly for the following four weeks. Then, the treatment was switched to the neem-derived prodcut, Aza-Direct, for the remainder of the cover sprays until mid-August. The Surround-only program received 13 applications over the course of the season, while the combination program received 5 applications of Surround and 8 applications of Aza-direct.
The reasoning behind the treatments was that kaolin would deter plum cucurlio oviposition, so it was used in both treatments until the degree day model predicted egg-laying was finished. The Aza-Direct was then applied to control the rest of the pest complex, while providing a comparison to the full-season program of Surround. Also in this orchard, two rows of 'Cortland' apples were excluded from these treatments and used for another trial on the efficacy of handgun applications of Surround and Aza-Direct against apple maggot and the later season generations of the complex of internal Lepidoptera (oriental fruit moth, codling moth, and lesser appleworm). These applications were made with a high-pressure (450 psi) handgun sprayer.
The Surround-only program was significantly more effective in controlling internal Lepidoptera and resulted in a higher percentage of clean fruit than the combination program of Surround and Aza-Direct (Table 1). Damage from other pests was not significantly different between the two treatments. The higher percentage of clean fruit in the Surround-only treatment was due to improved control of internal leps and plum curculio, as damage from other pests in the two treatments was similar.
Table 1. Fruit Damage
Means within a row followed by the same letter are not significantly different (Fisher's Protected lsd test, P <0.05). Data transformed (arcsine-square root) prior to analysis.
The late-season handgun sprays of both Surround and Aza-Direct were significantly more effective in controlling internal Lepidoptera than the airblast treatments (Table 2). The handgun sprays of Surround were also significantly more effective against apple maggot than the airblast sprays. The Aza-direct handgun sprays were not effective in controlling apple maggot in the sprayed 'Cortland' trees, but maggot damage in the 'Delicious' apples treated with airblast sprays was significantly lower than that in the handgun plots. It is unlikely that the lower damage level in the Aza-Direct airblast treatments was due to the effectiveness of the sprayer, as most studies conducted in the past have shown that handgun sprayers provide more complete coverage than airblast sprayers. Therefore, these differences between apple maggot damage levels in the different application methods of Aza-Direct were probably due largely to differences in infestation levels in the two cultivars. 'Cortland' apples, which had the highest infestation levels in the handgun sprays (42%), are generally considered to be more susceptible to apple maggot than 'Delicious'.
Table 2. Handgun vs. Airblast Treatments
* Data taken from 'Cortland' trees
** Data taken from 'Delicious' trees
Means within a column followed by the same letter are not significantly different (Fisher's Protected lsd test, P <0.05). Data transformed (arcsine-square root) prior to analysis.
In this study, less than half of the harvested fruit was free from insect damage in trees treated with a conventional airblast sprayer. Although there were no unsprayed check trees left in the orchard to estimate insect pest population levels, observed damage levels and evaluations of harvested fruit taken from the orchard in previous years indicate that indigenous pest pressure within this orchard is very high. Obviously, it is very difficult to protect fruit in heavily infested orchards with available materials certified for use in organic programs. The two materials evaluated in this study are probably some of the best insecticides currently available to growers opting to appeal to an organic market. Application technology for these particular products has not yet been perfected, but this study has shown that handgun spraying results in substantially better control of two key direct pests of apples, apple maggot and plum curculio, particularly in the case of Surround. Although handgun applications were not evaluated in this study against the plum curculio, previous studies conducted in a heavily infested research orchard at the Geneva Station have shown that handgun sprays of Surround were very effective against all direct fruit-feeding insects, including the plum curculio. Therefore, applying sprays of Surround with a handgun may be an option for growers seeking to increase the amount of insect-free fruit in their organic orchards.
Identification of adequate markets for fresh organic apples in the Northeast is another challenge for organic producers. Most organic fruit in this region is sold for processing, and there are small niche markets that offer limited amounts of fresh fruit. However, organic apples are usually sold at prices 2-3 times higher than conventionally grown apples. By increasing the percentage of clean fruit, the grower also increases his profit margin, but this may still not be enough to make this system economically feasible.
These organically approved insecticides are about five to six times more expensive than conventional products (Table 3). Also, more frequent, sometimes weekly applications are required, and labor costs for these treatments are naturally more expensive, especially if handguns are used. These high labor costs for organic production apply not only to pesticide applications, but also to hand-thinning, hand-weeding, and harvesting. Other inputs such as increased fuel, water, and equipment wear should also be considered.
Table 3. Pesticide Cost Analysis
* Prices quoted from UAP Northeast 10/19/01
Organic production does have positive aspects as well. If the quality of fruit is high enough, the price it fetches may cover the input costs and still make a profit for the grower. Competition for the organic market is small, and consumers concerned about the pesticides used in conventionaly grown crops are probably willing to pay more for certified organic products. This increased interest by both the grower and consumer then prompts not only the apple industry but also researchers to develop better materials and techniques. Also, most of the organically certified materials tend to be "softer" and offer more of an opportunity for biological control, further reducing the amount of pesticides needed.
Because of the complexities associated with organic production systems, a grower must be prepared to make a substantial investment to enter into this market. The increasing interest of organic consumers has had an effect on the number of farmers attempting to grow organic produce. With the development of more efficient materials and techniques, producing a high quality certified organic product might be possible. However, consumers willing to pay premium prices for this type of produce will be the driving factor behind future organic markets.
This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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