Dr. Charles J. Masters, Technologist, Weyerhaeuser Company
Seed damage by the Douglas-fir cone gall midge (DFCGM) (Contarinia oregonensis Foote) is a major cause of reduced seed yield in orchards of Douglas-fir. Infestations of this critter have destroyed up to 80 percent of the seed in some crop years.
About Douglas-fir Seed Orchards
The Value of Quality Seed
Losing 80 percent of a crop is no small matter. When DFCGM infestations are high, their damage translates into significant economic loss for Douglas-fir seed orchards. Not only does the loss of seed increase the cost of the seed that is harvested, the average genetic value of the remaining seed is reduced by the indiscriminate feeding. The resulting seed is lower in quality, resulting in less wood at harvest time. Inferior seed leads to other problems, such as delays in meeting projected growth milestones, adding an additional economic burden for some land managers.
The Opportunity Lies in the Duff
The Douglas-fir cone gall midge is a nasty little critter indeed, if you are in the business of producing seed. The adult emerges during the period Douglas-fir flowers are open and receptive to pollen. The female lays her eggs on the developing cone scales near the seed. Following egg hatch, larval feeding on the scale tissue stimulates the formation of a gall, which encases the developing insect and either restricts the development of the seed or fuses the seed to the scale making extraction impossible. In the fall or winter, after the dry cones have become wet by rain, midge larvae drop from the open cones onto the duff or the orchard floor and overwinter in the spent pollen buds. It is this aspect of the DFCGM life cycle that the pest should have reconsidered before deciding to inhabit a seed orchard.
Orchard managers have long known gall midge larvae are concentrated in the duff layer beneath trees for several months of the year while overwintering. This aspect of its life cycle was thought to be an opportunity for cultural control. However, it wasn’t until relatively recently that the motivation and resources existed to exploit this. Small-scale studies on the manual removal of duff were initiated in 1994 by entomologists Christine Niwa, U.S. Forest Service (USFS) Forestry Sciences Laboratory, Corvallis, Oregon, and Dave Overhulser, Oregon Department of Forestry. They confirmed that a reduction in the number or weight of spent pollen cones from the duff layer resulted in a significant reduction in adult midge emergence. Over the three years of study, this manual removal of duff reduced emerging gall midge populations by an average of 55 percent compared to untreated check areas. In a subsequent study, results showed again a direct relationship between the removal of pollen cones and reduced midge survival. This study also confirmed that spent pollen cones are critical overwintering sites both in natural duff and over bare ground.
The Operational Challenge
Our first attempt at operational duff manipulation and removal in an orchard was initiated in 1998. We secured funding from private industry as well as state and federal government agencies. We used these funds to purchase a used Rac-O-Vac Turf Sweeper and to modify it for vacuuming and removing duff in an orchard setting. The USFS Equipment Development Center in Missoula, Montana, designed and implemented the modifications under the direction of Keith Windell, Project Engineer.
The operational trial of this sweeper consisted of three treatments, each replicated ten times. The treatments were: (1) using a flail mower to loosen the duff and then vacuuming, (2) flailing only for disturbance, and (3) an untreated control. For each treatment and replication, the equipment made one pass on the aisle sides of two neighboring orchard trees between the bole (trunk) and the drip-line of the crown in the fall of 1998. Eight midge emergence traps per replication were placed in the treated areas in April of the following year; these were monitored for midge emergence through the middle of May. Statistically significant treatment differences in midge emergence were observed with a 75 percent reduction in emergence in the flail-plus-vacuum plots compared to controls. We were able to significantly reduce midge emergence operationally, but two important questions remain to be answered.
Taking It Into the Orchard
In preparation for future testing designed to answer the above questions, we conducted field trials comparing the Rac-O-Vac Turf Sweeper and a Tuff Vac 5000. Our objective was to determine which machine had the strongest vacuuming ability and the best orchard maneuverability, and which would adapt most readily for materials handling and disposal. We decided to go with the Tuff Vac 5000.
We secured funding for equipment modifications from the states of Washington and Oregon, from federal government agencies including the USFS and the U.S. Environmental Protection Agency (EPA), and from the Washington State Commission on Pesticide Registration.
At this writing, modifications to the Tuff Vac 5000 are nearing completion. We have designed and fabricated a bin and dumping mechanism for the Tuff Vac, have purchased a self-dumping trailer, and have fabricated side panels for the trailer. We plan to initiate an operational trial with the modified equipment in October 2003.
Developing integrated pest management approaches to resolving pest problems takes a significant investment of time and money. However, given the high priority we are placing on environmental protection and minimizing risks to human health, researching and implementing integrated strategies is the only prudent course of action. DFCGM and the rest of you critters, beware! We are up to the challenge.
Chuck Masters is with the Weyerhaeuser Company and serves as the Forest Protection representative to the Washington State Commission on Pesticide Registration. He can be reached at (360) 330-1736 or firstname.lastname@example.org.
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David Granatstein and Dr. Carol Miles, Center for Sustaining Agriculture and Natural Resources, WSU
One of the fastest growing segments of agriculture in the United States is organic farming. For the past decade, the organic food industry has been growing at a rate of 20 to 30% annually, with a commensurate increase in land farmed under certified organic management and an increasing need for research and education on organic farming practices and systems. While certified organic farming is now specifically defined by the USDA National Organic Standards, many practices that are central to organic farming are being incorporated by farmers into their “conventional” systems to help meet economic and environmental goals. Similarly, research developments in “conventional” agriculture on biointensive IPM and biological control, for example, are expanding and are of direct benefit to organic producers. Thus, the commonality between “organic” and “conventional” is increasing.
At Washington State University, the Center for Sustaining Agriculture and Natural Resources (CSANR) is developing a research and education program on Biologically Intensive and Organic Agriculture (BIOAg) to encourage this common ground that can help all producers while clearly addressing public concern for environmental stewardship. The need for a more sustainable agriculture will require greater reliance on biological processes that are renewable, that are non-polluting, and that provide multiple benefits for farmers and society; hence the term “biologically intensive.” Organic farming is one of the better developed examples of this concept. Land grant universities such as Washington State University (WSU) are helping to meet the growing need for this type of information.
Seeds of the Symposium
A common misperception in the Pacific Northwest is that the land grant universities are not involved in organic farming research. In 2001, CSANR conducted an informal email survey of WSU agriculture faculty to determine the kinds of organic or organic-related projects, if any, they had completed, were underway, or were planned. Over 50 faculty members responded to the survey and reported 90 projects that related to organic agriculture. In October 2001, the CSANR hosted a day-long meeting where 50 faculty participated to plan organic farming research and education at WSU. The group proposed a symposium as a next step to bring researchers and their projects together with growers, educators, and consultants. Two goals were identified:
Planning for the Northwest Symposium on Organic and Biologically Intensive Farming became a team effort involving WSU, Washington Tilth Producers (a statewide sustainable/organic farming group), Oregon State University, and Oregon Tilth. The Symposium date was set to occur the day before the annual Tilth Producers Conference to provide as much crossover of participants as possible. A planning group consisting of university, non-governmental organization (NGO), grower, and industry representatives designed an agenda consisting of presentations on four key topics related to BIOAg, followed by a two-hour interactive poster session. The topics were soils, seeds and genes, pest management, and system studies. Speakers were selected to represent leading edge research. More practical presentations on organic farming methods occurred during the Tilth Conference itself. Funding for the event was provided by registration fees, an EPA mini-grant, CSANR, Western SARE, and contributions from industry sponsors.
Fruits of the Symposium
Branches of the Symposium
In the oral presentations, Chris Koopmans, from the Louis Bolk Institute for Organic Farming in the Netherlands, described his work on field measurement and modeling to predict soil nitrogen dynamics on organic farms. He is working with the NDICEA (Nitrogen Dynamics in Crop Rotations in Ecological Agriculture) simulation model that tracks soil nitrogen, organic matter dynamics, and crop uptake. The goal is to identify the nitrogen release characteristics of various organic fertilizers and use the model to best match fertilizer type and timing with crop need while minimizing residual nitrogen at the end of the growing season.
Steve Jones, WSU wheat breeder, highlighted his organic wheat breeding and perennial wheat development projects. His group is screening over 160 historical cultivars previously grown in the Pacific Northwest for traits of potential benefit to organic farmers, such as emergence rate, height, and resilience to mechanical weeding. John Haapala introduced the Farmer Cooperative Genome Project that he initiated, with organic growers across the country evaluating vegetable germplasm in cooperation with Cornell University Vegetable Breeders Institute. Results include powdery mildew resistance for squash and cucumbers, blight-resistant tomatoes, and a new organic broccoli breeding effort at Oregon State University.
Advances in biointensive IPM of insects in tree fruit were presented by Ted Alway, including area-wide mating disruption and the role of surrounding habitat for natural enemies. His Wenatchee Valley Pear IPM project illustrated potential lower cost and better pest control with an “organic” insect pest management program. Matt Liebman, Iowa State University agronomist, illustrated his years of work on integrating crop, soil, and weed management to make systems more “weed suppressive.” He uses the term “many little hammers” to illustrate the need for multiple strategies that each deliver small gains in weed control rather than a “big hammer” replacement for herbicides.
Two contrasting farming systems studies were also presented. A field-scale replicated orchard systems experiment led by WSU’s John Reganold that included conventional, organic, and integrated production, has shown the organic system to have tree growth, fruit yield, and quality equal to the conventional system. Using the “Responsible Choice” environmental impact tool, he compared the three production systems. The Responsible Choice method assigns a numerical value to a range of factors pertaining to the pesticide such as acute LD50, effect on beneficials, and solubility, then combines these to arrive at a score. Using this method, Reganold found the organic production system to have the lowest impact and the conventional the highest.
The other farming system study was presented by Henning Sehmsdorf who introduced his integrated small farm where he is monitoring nutrient, energy, labor, and cash flows in his quest for a highly productive and renewable farm model. He and his colleagues used emergy analysis to evaluate ecological sustainability on the farm. (Emergy is defined as the available energy of one kind previously used up directly and indirectly in the production of a product) Vegetable, fruit and pork production required large amounts of imported resources in relation to the amount of locally available emergy that those sub-systems received from the environment. In contrast, beef, lamb, and grain production relied much more on local resources.
Offshoots of the Symposium
Future symposia are envisioned as a continuation of this initial cooperative effort. Rather than a broad range of topics, they will likely be organized around priority issues facing BIOAg, such as the potential convergence of organic farming and direct seeding. The first Symposium set in motion many new “biological connections” among the people who will shape a more sustainable agriculture in the region.
David Granatstein is a Sustainable Agriculture Specialist with WSU’s CSANR. He can be reached at the Wenatchee Tree Fruit Research and Extension Center at (509) 663-8181 or email@example.com.
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Dr. Joan R. Davenport, Soil Scientist, WSU
Two types of grapes are grown in the irrigated areas of central Washington State: wine grapes and juice grapes. There are both similarities and differences between these crops. The amount of acreage in the state planted to each is fairly similar, with approximately 25,000 acres planted to juice grapes and 28,000 acres to wine grapes.
The Business of Grape Growing
When producing grapes, it is standard practice for the grower to “contract” (i.e., pre-sell) his grapes to a processor. The processor might be a juice, jelly, or juice concentration facility in the case of juice grapes, or a winery in the case of wine grapes. The terms of the contract will specify yield and quality, although the parameters between the two types of grapes are different. With juice grape production, growers must attain a minimum sugar content (known as BRIX) before they can harvest their crop or they will receive a quality penalty from the processor. Beyond that, juice grape growers get paid by the ton; the more tons the better. On the other hand, in wine grape production, producing high tonnages can actually result in cost penalties. Wine grape quality is a more complex equation, one that is determined by the winemaker. The winemaker looks for optimal (not necessarily highest) fruit BRIX and acid levels, which vary with the grape variety, but the wine flavor is what really makes or breaks the grade. Essentially, when a wine grape grower delivers a crop that ends up in a reserve bottle of wine, the grower gets paid more for his crop. The trick with wine grape production is to yield high quality and enough fruit to make the process economically viable.
Whether wine or juice grapes, all grapes require adequate nutrients and water to sustain production in order to meet contracted yields and quality parameters. Adequate and uniform nutrients also play a role in pest management; any area of the vineyard that is weakened by inadequate nutrient supply is more likely to be susceptible to pest pressure. The more that can be done to make the vineyards uniform, the better chance the grower will meet yield and quality goals.
Working Toward Uniformity
A certain degree of uniformity in yield and quality is an economic necessity for the grape grower. Many factors contribute to variability, including plant nutrient availability across the vineyard. Plant-available nutrients come both from applied fertilizer and from chemical properties inherent in the soil. The inherent chemical properties vary across a field. Not only do specific nutrients vary, so do properties such as pH (acidity/alkalinity) and organic matter, each of which further influences plant nutrient availability.
In a vineyard setting, nutrients typically are applied at a uniform rate across an entire field or large sections of a field. If the inherent properties of the underlying soil vary to begin with, such uniform application will not decrease this variability. Because of likely links between nutrient variability and yield/quality variability, soil scientists have long sought ways to manage nutrients differently across fields.
Pruning Study Led to Nutrient Study
In a study published in 1999, researchers Robert Wample, Lynn Mills, and I found a great deal of yield variability in Concord grapes that was not related to the pruning treatments we were studying (Wample et al. 1999). In an effort to understand and eventually reduce the variation in yield and quality across a vineyard, we developed a companion study to evaluate our ability to reduce yield variability. The mechanism we chose was variable rate fertilizer applications.
Technological advances over the previous decade enabled us to consider practical application of fertilizers at varying rates across a field. In the late 1980s, variable rate application (VRA) fertilizer equipment was developed for large scale, row crop farming. In the late 1990s, a VRA fertilizer spreader was developed commercially for narrow-row (ca. 9 ft) fruit crop systems.
VRA technology uses tools known as Global Positioning System (GPS) and Geographic Information System (GIS) to guide fertilizer application. The concept behind VRA fertilizer equipment is to assess the availability of nutrients in the field by collecting soil samples from spots that have been mapped using GPS latitude and longitude coordinates. Then, once the plant-available nutrient status throughout the field is known, a map is made using the GIS to tell the fertilizer application equipment how much nutrient (fertilizer) is needed in the various places throughout the field. The map and the GPS combine to increase and decrease fertilizer amounts applied as the spreader drives throughout the field.
VRA Study Parameters
To evaluate the potential for VRA fertilizer application in Concord (juice) grape, we did several things:
We sampled soil intensively from a ten-acre vineyard block from March 1998 through March 2002 (Figure 1). Based on the results from the soil tests, nitrogen (N), phosphorus (P), and potassium (K) fertilizers were applied at variable rates across the field using a commercially available VRA orchard spreader in the 1998 through 2001 growing seasons. A soil sample taken the following spring (before bud break) was used as an indicator of change in soil test values associated with the variable rate fertilizer application. For example, the 2002 soil sample would be an indicator of the changes from 2001.
Finding the soil pH values to be fairly high, we made a blanket application of 500 lbs/A sulfur to the field in both 1998 and 1999. Our goal was to bring the pH values to between 7 and 7.5.
In addition to the fertilizer applications, we monitored crop yield using commercially available yield monitoring equipment. Results were used to evaluate the impact of the nutrient management practices on the crop.
There are a number of ways to measure variability. Due to the limited number of points we measure in this field, we chose to use a very standard statistical measurement to express variability – the coefficient of variability (CV). In general, the higher the CV is, the higher the variability. However, it is not fair or useful to compare the CV for something like yield to the CV of something like soil test phosphorus since the units in which we measure each are different.
Over the four years this project was conducted, variability in yield increased and decreased in alternating years. For example, in the first year of the study (1998) variability in yield was lower than in the previous year but in the second year (1999) yield variability was almost as high as two years before (Table 1).
Variability in the soil chemical properties most closely related to the VRA nutrient management proved interesting. In general, variability of nitrate nitrogen (the type of nitrate we measure in soil tests) decreased with time until the last year of the study (Figure 2). The dramatic increase in nitrate variability in 2002, especially in the subsurface soil, is probably related to water management. During the 2001 growing season, the commercial farm on which this research was conducted converted from rill to overhead sprinkler irrigation. Moisture monitoring data showed much higher water content in the lower soil depths than in the previous years. Since nitrate is very mobile, the extra water likely moved it more deeply than in previous years. If the applied nitrogen fertilizer moved outside the root zone of the plant, this would reduce the plant’s ability to utilize it.
Neither potassium nor soil pH variability (Figures 3 and 4) changed much over the course of the study, although soil pH values changed a great deal. On the other hand, if anything, soil phosphorus variability increased with time (Figure 5).
Using variable rate nutrient management did change the overall fertilizer use during the four years of this study. Table 2 shows the predicted total amount of fertilizers N, P, and K that would have been applied across all four years if the average value of all of the soil tests were used compared to the actual amount used with VRA application.
Soil test phosphorus values on this site were high in all years. As a result, we applied more P with VRA than would have been applied based on the field average. More potassium was applied with VRA as well. However, using VRA for N resulted in a significant reduction in N over the course of the study.
Given that VRA did not result in any improvement in P or K variability, using this technique does not seem to be an advantage for these nutrients. However, with N, variability decreased, as did fertilizer use, indicating that VRA for N is a viable practice in juice grapes.
Joan Davenport is a Soil Scientist with Washington State University’s Irrigated Agriculture Research and Extension Center in Prosser. She can be reached at (509) 786-2226 or firstname.lastname@example.org.
Wample, R. L., L. Mills, and J. R. Davenport. 1999. Use of precision farming practices in grape production. p. 897 - 905 In P. Robert, R. H. Rust, and W. E. Larson (eds). Proc. 4th Intl. Conf. on Precision Ag., Minneapolis-St Paul July 19-22, 1998. ASA/CSSA/SSSA Press, Madison, WI.
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