April 15, 2002 Volume 11 No.5 Update on Pest Management and Crop Development
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TRAP CATCHES (Number/trap/day)
(Dave Rosenberger, Plant Pathology, Highland)
This work was supported by the New York State Integrated Pest Management Program.
Apple scab ascospore counts as determined from squash mounts:
The spore counts shown above are of primarily historical interest because warm temperatures over the past five days, combined with extended wetting over the weekend, have promoted rapid ascospore maturation. The warm wetting periods provided ideal conditions for establishing early season scab infections. The high temperatures predicted for this week will ensure continued rapid development of scab spores throughout the state.
In areas of the state where green tissue was present, growers who failed to apply a protectant before the rains have a significant risk of primary scab unless they can cover orchards with strobilurin or SI+contact fungicides within 72 to 96 hours after the start of the first infection period. Growers who find it impossible to cover orchards within 96 hours should apply an SI+contact spray as soon as they can, even if that spray is applied more than 96 hours after infection. SI fungicides applied after 96 hours will still arrest fungal development provided the orchard does not already contain threshold levels of SI-resistant scab. Where only moderate levels of SI resistance are suspected, using SI's at maximum label rates can boost activity of the SI sprays. In orchards where scab is fully resistant to SI fungicides, maximum label rates of strobilurin fungicides should provide 7296 hours of post-infection activity, but lower rates may prove disappointing if applied more than 4872 hours after infection. The strobilurins do not have "pre-symptom" activity, so there is little point in applying strobilurin fungicides more than 96 hours after infection.
In Highland, we had three separate scab infection periods: The first began Friday afternoon with a light drizzle. The second began Saturday afternoon, and the third began Sunday night. All three qualified as moderate Mills infection periods because mean temperatures were in the upper 50's and low 60's, but all three might be considered "marginal" infection events for other reasons. Total rainfall during the first infection period was only 0.03 inch and may not have been sufficient to generate a significant spore discharge from the dry and brittle leaf litter. The second infection period started about 4:30 pm and came with 0.13 inch of rain, but in some locations drying may have occurred near midnight, thereby limiting the severity of this infection period. (We counted this as a moderate Mills period based on partial leaf wetting through 4:30 AM. The third infection period can be discounted because wetting started after dark and no significant level of spore release would have occurred in the dark during this very early part of the season. Furthermore, because dry weather in the Hudson Valley had slowed spore maturity, the importance of these early infection periods is less clear than for most other regions within the state where spore maturity was more closely aligned with tree phenology.
Hudson Valley growers were advised to spray, either before or immediately after the rains, any orchards that had scab last year, orchards (or orchard rows) within several hundred feet of abandoned orchards, and perhaps in blocks of highly susceptible cultivars such as Jerseymac, GingerGold, and McIntosh. Some Hudson Valley growers will gamble on leaving other orchards unprotected until later this week because the marginal nature of the past weekend's infection periods, the delayed spore maturity, and the relative lack of inoculum in most orchards due to dry weather last year. Only time will tell if the gamblers are making the right decision.
(Bill Turechek, Plant Pathology, Geneva)
Weather plays a critical role in the daily activities of a grower. Orchard care, fertilization and, perhaps most critically, pest management are all governed by weather. Most growers do not rely on regular calendar applications to manage pests, but try to time important fungicide and insecticide applications based on the weather. In fact, growers who rely on disease forecasting models to time applications know that nearly every model or predictor that forecasts plant disease requires reliable weather information. For example, the MARTBLYT model used to predict blossom blight infection of fire blight of apple and pear requires readings of the daily high and low temperature and measurements of precipitation in the form of rainfall or dew. The Venturia inaequalis (apple scab) ascospore maturity model requires daily readings of temperature.
So how does a grower collect reliable weather data? Weather data can be collected in two basic ways: it can be collected from on-farm instrumentation or from offsite instrumentation. The benefit of using onsite weather equipment is that instruments can be placed at locations that historically have higher levels of disease pressure and will enable you to closely monitor conditions. Weather data collected from offsite instrumentation can be very representative of your farm if the instrumentation is located nearby. Offsite data can be delivered via telephone, fax, telemetrically, and via the internet and can be done so at a frequency as little as once per day to being available nearly instantaneously. Nonetheless, depending upon the quality of the instrumentation and the weather variables measured, measurements made on farm are unquestionably the most representative of your farm.
Yet, in the grand scheme of pest management the question arises: How accurate does weather data need to be? Do you need to record temperature to an accuracy of 1 degree? Does it make a difference if 1 inch of rain fell versus 1.25 inches? For plant diseases the answer is "it depends". It depends upon the disease(s) of concern and the models that you are running. Therefore, every grower must make the decision on how valuable precise weather data is to them.
The basics to weather monitoring begin with measurement of temperature, usually the day's high and low are of greatest importance, atmospheric and free moisture (e.g., relative humidity and rain), and leaf wetness. There are many makes and models of instruments capable of recording these variables and some of these will be discussed in what follows.
Temperature is the environmental variable that is often most correlated with a biological response and is nearly universally included in forecasting models. Several types of thermometers are available to measure temperature. Liquid-in-glass thermometers are the most widely used. Most thermometers now use alcohol (rather than mercury) as a medium and are calibrated to a precision of around 0.5C. Thermometers should be placed strategically throughout the farm, particularly in low-lying areas where frost is a danger, as those few degrees of variability at lower temperature can be quite critical. Thermometers, particularly high-low thermometers, must be read daily in order to retrieve the data, which can be a cumbersome chore. Otherwise, errors with this type of thermometer are often associated with poor readability, radiation, or through parallax (i.e., not reading the thermometer on a line parallel to the top of the liquid column). Deformation thermometers include the bimetallic strip and Bourdon tube thermometers. The bimetallic strip thermometer measures the linear deflection between the bond of two metals with different thermal coefficients that is caused by a change in temperature. The deflection is recorded mechanically to a strip chart recorder (e.g., hygrothermograph). Similar thermometers are available that measure the deformation of a gas or liquid. These thermometers are similar in accuracy to liquid-in-glass thermometers, but have a slow response time and are also sensitive to solar radiation. These thermometers are most useful in controlled environmental studies where a record of the temperature is needed.
Thermocouples and thermistors are electric thermometers that are well suited to automatic recording and logging data for computer usage. Thermocouples are junctions of dissimilar metals that generate an electromotive force proportional to their temperature at the junction (Campbell and Madden, 1990). Thermistors are semiconductors of ceramic materials made by sintering (i.e., heating until a substance becomes a solid without melting) mixtures of metal oxides (e.g., manganese, nickel, cobalt, iron, copper, and uranium). The electrical resistance of a thermistor is inversely proportional to temperature. Thermistors and thermocouples can record temperature to an accuracy of 0.1C but to ensure accurate readings, electric thermometers should be aspirated, shielded from sunlight, and protected from wetness. Different types of shields are available for the different types of thermometers.
Atmospheric and free moisture are key variables in the infection process of many fungi and bacteria. Relative humidity, leaf wetness, rain, and soil moisture are the variables typically measured to quantify the level of moisture in the environment. Relative humidity (RH) is the ratio of the amount of water vapor in the air (i.e., vapor pressure) to the amount of water vapor that the air could contain at that temperature (i.e., saturation vapor pressure). Psychrometers (e.g., the sling psychrometer) measure the difference between the air temperature and the temperature recorded by a wet-bulb thermometer (a measurement of evaporative cooling) to provide a measure of the relative humidity. To obtain accurate measurements of RH with a psychrometer, thermometers capable of recording to an accuracy of 0.1C should be used. Electrical sensors that operate by measuring the change in resistance of water adsorbed to some material are used more commonly to measure RH. Electric sensors take several minutes to accurately respond to a change in RH, but this is typically not a problem in most agricultural settings.
Leaf wetness is a key variable driving foliar plant disease epidemics. Leaves may become wet from dew, fog, guttation water, irrigation water, fungicide, insecticide and fertilizer applications, and, of course, due to rain. Leaf wetness continues to be one of the most difficult parameters to measure because it is itself so variable within the plant canopy. Three general approaches are used in measuring leaf wetness. The deWit leaf wetness sensor mechanically measures leaf wetness by measuring the contraction and expansion of a hemp string or some other element as it responds to wetting and drying. Electric sensors are the most popular. Electric sensors consist of at least two electrodes (e.g., strips of nickel, wire, etc.) that are mounted in parallel on artificial leaves made from circuit board, plastic, cloth, or other type of synthetic material designed (to some degree) to mimic surface characteristics of a leaf. The circuit is completed upon wetting, and the extent of wetting is measured by electrical resistance. However, leaf wetness sensors fall short in capturing the biological and micro-environmental variability found within a canopy, thus careful interpretation of the data reported by leaf wetness sensors must be exercised. Leaf wetness can also be estimated, but this is not widely used. For example, the number of hours above 90% RH has been used to derive an estimate of leaf wetness.
Rain not only contributes directly to leaf wetness, but serves as a major means of disseminating fungal propagules. Indeed, some of our most serious diseases are almost exclusively splash-dispersed and the degree of dispersion is directly related to the amount, duration and intensity of the rainfall. Rainfall can be easily and accurately measured with a number of different types of rain gauges. Rain gauges, however, must be visited shortly after the rain event and provide only a measurement of the quantity of rain that has fallen. Tipping-bucket rain gauges are used in electronic setups and provide measurements of rainfall amount, usually to an accuracy of 0.01 inch, as well as the duration of the rain.
Soil moisture is important in studies of root diseases. Soil moisture is probably the most neglected measurement of moisture because it is difficult to quantify accurately. Electric sensors are available for the quantification of soil moisture.
A number of electronic sensors are available that are capable of recording and logging virtually every weather parameter including temperature, relative humidity, rainfall, leaf wetness, light intensity, and soil temperature. These products range in their complexity as well as in their price. In short, recording devices are typically very accurate and can record at intervals as short once per every half-second to once every few hours. At longer recording intervals, some of these sensors can go on recording for years before running out of space! Most sensors, however, require you to download the information, usually into a portable "shuttle", and then transfer the information from the shuttle to your computer. This is not difficult; however, if you want to collect information daily, this can even be even more cumbersome than using simple instruments, especially if temperature is the only parameter that you are interested in. But if you do not need to collect information every day and/or more than one weather parameter is utilized and/or you are using your weather data to run various computer-driven disease or insect models, then using electronic sensors may be your best choice.
Weather equipment can purchased from a number of companies, including A.M. Leonard, Inc. (http://www.amleonard.com/main.html), Forestry Suppliers, Inc. (http://www.forestry-suppliers.com/), Orchard Supply Company (http://www.Orchardsupply.com), and Gempler's (http://www.Gemplers.com), just to name a few. Onset Computer Corporation (http://www.onsetcomp.com), producers of the Hobo series of data loggers, and Spectrum Technologies (http://www.specmeters.com/), producers of the Watchdog series of data loggers, offer a wide range of affordable sensors and sensor technology. Although not a realistic option for most growers, portable weather stations are available that can transmit weather data from the field to your computer via modem. These telemetric weather stations usually consist of a combination of the electronic sensors, like those discussed above, but are wired in such a way to deliver the data directly to your computer. Maintenance of the station becomes a chore and setting up the station can be complicated.
Detailed weather information can be obtained via the internet. There are a number of commercial and non-commercial sites that are set up to provide free weather information for virtually every town in the United States. Of course, weather stations are not deployed in every town across the United States. Rather, sophisticated algorithms are used to predict weather across a region from base weather stations (usually located at major airports). The algorithms are becoming remarkably more accurate and can provide quite precise information to a number of areas. Some of the most popular and informative weather resources on the web include:
The United States Weather Pages (http://www.uswx.com/us/wx/)
The National Weather Service (http://www.nws.noaa.gov/)
The Weather Underground (http://www.wunderground.com/)
NewsChannel 9 and Niagara Mohawk "Niagara Mohawk LIVEDoppler 9" (http://www.wixt.com). Radar Images on this website are updated every 10 minutes
Becoming more popular are sites specifically designed to serve agriculture. Usually for a fee, these sites will provide current weather information, but more useful, they run a number of plant disease and insect forecasting models and provide recommendations based on their output. Some of these sites are set up to deliver personalized data to your email each morning and some provide colorful maps that detail pest pressure that can be viewed over the internet. Two of these companies that serve NY are the Northeast Weather Association (NEWA) and Skybit.
NEWA (http://www.nysipm.cornell.edu/newa/index.html) is a consortium of growers who have installed small weather stations on their land. Each day, information such as the temperature, relative humidity, leaf wetness and precipitation is transmitted from the farm to the Agricultural Experiment Station in Geneva. There, the raw data is processed by several computer programs, each designed to evaluate the data and issue a pest forecast specific to the area where the fruit or vegetable grows. A grower can either choose to find the daily information from a personal computer or opt to have a forecast sent via facsimile.
SKYBIT, Inc. (http://www.skybit.com) is a ten-year-old company specializing in development of site-specific weather products for agriculture, energy, and other industries. SkyBit, through its E-Weather Service and research programs, can provide custom data sets for weather-dependent decisions. E-Weather Service "Ag-Weather" has been supporting the agricultural community weather information needs for more than 6 years. A variety of products have evolved over the years to assist decision making in the field. These products include integrated pest management (IPM) simulation and forecast, irrigation schedules, frost predictions for select crops, as well as custom data for other commodities.
WHO LET THE BUGS OUT?
(Art Agnello, Entomology, Geneva)
Our annual sneak preview of summer weather is slated to hit this week, and insects, as the original sun-worshippers, are certain to respond with a burst of activity characterized by those things they do best -- fly, mate, infest. Together with the generally accelerated tree growth and last weekend's disease infection periods, most growers will have a full plate, so here's a brief checklist of some potential prebloom arthropod concerns to consider before the season gets away from you.
Mites: Oil applications should go on before we reach pink, and as there's no freezing weather forecast, any calm period of sufficient duration would be a suitable spray window. Start with 1.52.0% at the beginning of the week, and reduce to 1.01.5% as the trees reach tight cluster. Savey and Apollo can be delayed until pink, and if everything else runs away with your time and a miticide application before bloom is impossible, consider Agri-Mek at petal fall in problem blocks. Besides saving some time during the hectic pre-bloom period, this is also an ideal rotation material for purposes of resistance management.
Rosy Apple Aphid: In particularly susceptible varieties (Cortland, Ida Red, Golden Delicious, R.I. Greening), a material such as Lorsban or Supracide can provide effective prevention through tight cluster, and will pick up any San Jose scale at the same time.
San Jose Scale: Besides the Lorsban and Supracide noted above, delayed dormant oil applications will do a good job of reducing scale populations. If you're not treating for rosies but are concerned that SJS might be increasing in some blocks, Esteem is a new insect growth regulator with good activity on scale. The label calls for it to be mixed with oil, so if you're applying oil for mites anyway, this might be a tactic to try in severe cases.
Dogwood Borer/American Plum Borer: A coarse spray of Lorsban directed at trunk burr knots between half-inch green and petal fall is effective against both species that can be a problem in dwarf plantings.
Pear Midge: The first adults generally appear when Bartletts and Clapps are in the swollen bud to tight cluster bud stage, but no successful egg-laying occurs until the flower buds are a little more developed. In pear blocks with a history of midge infestation, concentrate on those portions of the orchard most protected from the wind by trees, high ground, or buildings, as the midges tend to be most numerous in these spots. Organophosphates like azinphos-methyl are the most effective materials; 2 sprays are recommended, one between late bud burst and first separation of the sepals, and another 7 days later (or at white bud, whichever comes first).
Pear Psylla: If you're just starting on your oil sprays, one application at 2% or two at 1% until white bud should provide adequate protection against egg deposition until an insecticide spray might be elected. Esteem at white bud or after petal fall has shown good activity in suppressing psylla numbers. Agri-Mek used shortly after petal fall has given good control if applied correctly (well-timed, adequate coverage, combined with an oil adjuvant), and split applications of Pryamite or Provado, also starting soon after petal fall, will keep nymph numbers down through the early summer.
Oriental Fruit Moth: The first adults could start flying within the next 7-10 days, depending on how long the warm stretch lasts, but we don't necessarily recommend pheromone disruption against this brood in peaches, as your plum curculio sprays will serve double duty against OFM as well; however, be prepared to start these at petal fall, as shuck split will be too late to get the first egg-laying moths. If for some reason you don't have to worry about curc, pheromones should be applied no later than the end of April.
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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