Comparison of Traditional to IPM Strategy for Managing Key Insect and Disease Pests of Raspberry, Meeker Variety – WSU Lynden, Wa.

Start Date and Duration

April through September, 1998

Investigators/Collaborators

Grower cooperators included Frank DeVries, Randy Honcoop, and David Youngquist. WSU personnel included Dr. Pete Bristow (Plant Pathologist), Dr. Lynell Tanigoshi (Entomologist), Craig MacConnell (Whatcom County Coop. Ext.) and Geoff Menzies (WSU Lynden Research Station Manager).

Project Description/How was it done?

Paired, 2-acre plots were selected on three farms; two in Whatcom County and one in Skagit County. Each plot was scouted regularly using techniques described in the WSU June, 1998 manual , Integrated Pest Management for Raspberries. Scouting was conducted by personnel from the Lynden Research Station who maintained regular communication with participating growers and researchers to share scouting results and facilitate spray needs and timing in the IPM plots. In the traditional plots, spray decisions were made by the grower. The intent of this project was to compare the efficacy and economics of a standard program to an IPM program which involved intense field data collection and group decision making.

Key scouting efforts included:

Four sampling sites, distributed throughout each plot were regularly sampled for the duration of the project. Each site was 2 post lengths (60 ft.) by 2 rows wide, with sampling conducted on the East side of one row and the West side of the neighboring row.

Field temperature recording devices called Hobos were maintained in each field to record air and soil temperature as well as relative humidity (2 of 3 fields). The purpose of these devices is to correlate heat accumulation with insect pest development and to assist in scheduling specific sampling efforts and treatment timing. At the beginning of the season, WSU personnel assisted cooperating growers with sprayer calibration to insure accurate delivery of pesticide product. This involved using a calibration worksheet and confirming actual sprayer nozzle output, and groundspeed. Spray records were kept for each farm and the cost of each program was estimated based on discussion with chemical suppliers.

Scouting was conducted between 15 and 20 times from early April through late August on these farms, with an average of 17 visits for the season, or about every 9 to 10 days on average. Sampling frequency was greatest in Skagit County where it was necessary to learn more about and accurately monitor orange tortrix leafroller development. This insect was not detected on Whatcom County farms. It took 45 minutes to an hour to sample each plot and therefore 1.5 to 2 hours per farm per visit. On those many occasions when leaves were collected for mite brushing and counting during and after harvest, there was additional lab time of approximately 2 hours per farm. The average number of visits during each crop stage was 3.3 visits prior to bloom (4/6-5/12), 5.6 visits during bloom (5/13- 6/22), 4.6 visits during harvest (6/28-8/10), and 3.3 visits after harvest (8/13-8/31).

Results

Sprayer Calibration

Time spent to calibrate sprayers was a very worthwhile exercise. It illustrated the importance of maintaining all components of the nozzles to insure proper output and the value of checking tractor speed and spray pressure in the field. Slight adjustments were made which improved the confidence of all of the collaborators. This exercise was very much appreciated by cooperating growers.

Spray Programs and Decision Making

Decision making in the IPM plots was based upon discussion of field data, grower experience and pest tolerance, intended markets, and input from researchers. Specifics are discussed below by pest category. In general, this project confirmed the variation that exists from farm to farm regarding pest density and pest species .This type of information is only learned through regular, annual systematic scouting. It was also made apparent to researchers that tolerance for both insect and disease pests is significantly lower in fruit destined for high end, fresh market and IQF (Individually Quick Frozen) markets compared to lower-end markets such as the juice market. This is reflected in the range of spray programs and expenses (see attachment). The most common difference between the IPM and Traditional programs was a reduced frequency of fungicide applications targeting fruit rot and spur blight in the IPM programs. In spite of this, the cost of pesticide materials was actually higher in the IPM program on 2 of the 3 farms. In one case, this was due to the decision to apply Vendex after harvest to suppress spider mites in the absence of predator mites and in the other it was the post-harvest application of Benlate to suppress cane blight infection of primocanes. Spray material costs/acre for the 3 farms on the Traditional plots were $148, $259, and $259 compared to the IPM plots which were respectively $153, $292, and $216. Cooperating growers were provided with scouting results in most cases which when combined with discussion with WSU personnel may have influenced their spray decisions in the Traditional plots.

Root Weevil Density and Development

Average black vine weevil (BVW) larval density in the top 6 inches of soil in late March and early April ranged from no detection to 3.5/sq ft. with "hotspots" within a field as high as 10/sq ft.. Weevils developed into pupae and adult stages slightly faster in Skagit than in Whatcom County fields (Fig. 1) The first emergence (Biofix) of adult BVW in Skagit County was on May 7, and in Whatcom County was on May 11. Adult weevils at this time are soft and have not begun to feed on the raspberry plant. Most adult BVW had completed emergence from the soil by late May to early June. Weevils develop rapidly in the soil as the soil temperature increases at that time.

 

Early Season Bud Damage

Early season bud damage from insects (climbing cutworms , clay colored or woods weevils) was not detected on 2 farms at all. Very light feeding by winter moth larvae and most likely clay colored weevil was detected on one farm in early to mid-April but only 1% of the buds examined were affected and treatment was not advised.

Pre-Bloom Fruitworm Evaluations

Using the beating tray, raspberry fruitworm beetles were detected on 2 of 3 farms at seemingly very low density(1-3 beetles/ 10 trays maximum, at usually 1-2 sites per plot). Five-minute bloom searches at each site were also conducted to assist with detection of this insect. In some cases, this procedure detected the insect when beating tray samples did not and vice versa. A single, early bloom (pre-bee) diazinon application was deemed necessary on 2 of the 3 farms where this insect was detected prior to bloom.

Bloom and Harvest Period Beating Tray Sampling

Adult BVW were detected with beating tray samples on 2 of 3 farms in mid to late-May. Counts generally increased by Mid-June with the highest count at any site of 5 BVW/10 trays. At this farm , night counts were compared to daytime counts , which revealed that sampling with a beating tray at night produced 3 to 10 times more BVW. On one farm, BVW was the dominant root weevil found. Another farm had a mix of BVW , strawberry root weevil, clay colored weevil, and woods weevils, and the third farm had a mix of clay colored weevil and rough strawberry root weevil. Pre-harvest Brigade applications were deemed necessary on all farms regardless of the weevil complex. The 2 machine-harvested fields were treated with a full canopy Brigade and the hand -picked field, where fruit was destined for the fresh market, was treated with a basal Brigade. There is a greater tolerance for most insects which reside in the canopy in fields which are hand -picked because they are less likely to contaminate the fruit. Post-treatment beating tray samples confirmed that all species of root weevils were well controlled with Brigade.

Leafrollers

Oblique banded leafrollers (OBLR), the most common leafroller found in Whatcom County did not reach significant levels in either field in Whatcom County. Trap catch peaked at 15 to 17 moths/trap in mid-June. Less than 4% of hills were infested with overwintering OBLR larvae in one field in mid-May and no infestation was detected in the other field. The recommended threshold for this insect is 10% infestation of hills. Pre-harvest Brigade sprays probably kill a large percentage of the adult population which is active in late June. Maximum trap catch was even lower in late August, peaking at 6 moths/trap.

OBLR activity was extremely low in the Skagit county field based both on trap catch and examination of lateral shoot tips during April and May. However, orange tortrix (OT) trap catch averaged well over 100 moths/trap/week from late April until late June (Fig. 2) .There was a major bertha armyworm hatch underway in mid-June. Emerging larvae were feeding on primocane tips resulting in up to 43% of hills being infested.This prompted Bt. applications in both plots. Javelin was applied in the Traditional plot and MVPII (microencapsulated Bt.) was applied in the IPM plot for comparison. The long-awaited OT larval hatch was detected in the third week of June, infesting 5-10% of hills on average. A second Bt. application was applied to both plots in late June to control both the armyworms and the OT larvae. This was followed shortly thereafter with a pre-harvest basal Brigade targeting root weevils. Early July sampling confirmed good control of OT larvae, presumably due to the Bt. Applications. Both formulations provided adequate leafroller control. The basal Brigade likely provided some control of bertha armyworms which migrate throughout the canopy.

Spider Mite Dynamics

As we have observed in the past, spider mite dynamics and interaction with predatory mites are highly variable from field to field. In the Skagit field, twospotted spider mites (TSSM) began to increase in late July (Fig. 3). In the IPM plot, counts increased rapidly to 40 mites per leaflet by August 10 with no response from predatory mites. Vendex was applied shortly thereafter. It suppressed the population for a week or so but TSSM rebounded by late August to 80 mites per leaflet. TSSM in the Traditional plot increased rapidly in mid-August reaching a density of 120mites per leaflet by the end of the month. This Traditional portion of the field was never sprayed. There was never a response from predator mites in either plot in this field.

In one Whatcom County field (Fig. 4), which has a recent history of yellow spider mite (YSM) infestation, YSM had increased to 40 mites/leaflet in mid-June. The population crashed following a full canopy pre-harvest Brigade spray but began to rebound in late July. There was a strong response from predator mites (PM) beginning in early July. PM continued to increase during August reaching a density of 8 PM/leaflet preying on a YSM population of 40 mites/leaflet/ in late August. This predator:prey ratio (.2) is favorable for biological control of spider mites. It was not necessary to spray YSM in this field.

The other Whatcom County field (Fig 5) had a low population (1-5/leaflet) of European red mites (ERM) during June and most of July. The population increased in August peaking at about 30 ERM/leaflet by the end of the month. However, due again to a strong response from PM throughout August, favorable predator:prey ratios (.05 to .3), and limited feeding damage for this late in the season, chemical control was not warranted. However, this was the highest recorded ERM population on raspberries in Whatcom County to date.

Spring Cane Disease Ratings

In early April, fruiting canes were examined and rated (scale of 0-3) for spur blight, cane blight, and cane botrytis. In this qualitative rating, 0=no detection and 3=widespread/severe disease incidence. There was minimal difference in the ratings within each field but there were differences between the 3 farms. Spur blight ratings ranged from 1.25 to 2.6. Cane blight ratings ranged from 0 to.75 and was detected on 2 of the 3 farms. Cane Botrytis ratings ranged from .37 to 1.5. It is interesting to note that the farm with the highest botrytis fruit infection in late June also had the highest degree of fruiting cane infection in early April. These ratings were useful in supporting the need for summer fungicide applications as well as specific post-harvest fungicide treatment of cane blight where present at a significant level in one of the fields.

Yellow Rust

The first field-detectable stage of yellow rust (aecia) was detected during the third week of April in Whatcom County fields during the 1998 season. With the exception of preventative Sulforix applications in the early spring, this disease did not require treatment in any of the 3 fields. Pressure was lowest in the Skagit field. In one of the Whatcom County fields we had the opportunity to compare a somewhat standard Sulforix timing and rate (March 30, 2 gal/acre) to a delayed timing and reduced rate (April 13, 1.5 gal/acre). On-farm research conducted in 1997 (Nooksack IPM Project) had shown that delaying Sulforix until average fruiting lateral shoot growth was 1-2" provided superior control of yellow rust. Field ratings of aecia in April and early May as well as counts of % infected primocane leaves collected for mite counting in August in the Traditional vs IPM plot showed improved yellow rust control once again with delayed timing. Although there was some initial burning of leaf margins in the delayed plot, there was no significant reduction of lateral length or number of flower buds compared to the traditional timing.

Botrytis Fruit Rot

The most important disease affecting raspberries during the 1998 season was botrytis fruit rot. In spite of various cultural practices, canopy vigor, and past fungicide practices among the cooperating growers in this project, this disease caused reduced fruit quality and forced each grower out of their intended markets and into lower value and lower net return markets just as peak harvest was getting underway and through the entire harvest period. Table 1 below shows botrytis fruit infection levels from the 3 cooperating farms in late June and mid-July.

Table 1

IPM Red Raspberry – 1998

Summary of fruit rot tests

B. Processing fruit **

* Berries harvested at the slightly pink stage of ripeness. Berries were picked directly into plastic clamshell packs. Berries incubated for 6 days and then evaluated for fruit rot (Day 1 at 32 F, Day 2 at 40 F and for Day 3 through Day 6 at 60 F).

** Berries harvested fully ripe. Berries placed individually on a wire screen in a moist chamber and incubated at 60 F for 3 days before being evaluated for fruit rot.

This evaluation shows that there was significant variation in the degree of fruit rot between farms in late June, but all farms were heavily infected regardless of the fungicide program in mid-July. There were some significant differences in infection between the IPM and Traditional plots in the June 30 processing fruit samples at both Whatcom farms. At Whatcom 1, fruit rot incidence was higher in the Traditional plot and at Whatcom 2, fruit rot was higher in the IPM plot. The fungicide spray programs were essentially the same at Whatcom 1. However, at Whatcom 2, there were 4 vs 6 captan sprays and 2 vs 3 Rovral sprays from early May through late June in the IPM vs Traditional plots.

Botrytis Fungicide Screening

This work is ongoing. Initial tests show that Botrytis isolated from each of these 3 farms is resistant to both Rovral and Benlate. This confirms earlier reports this season of Botrytis resistance to Rovral. Resistance to Captan is being tested at this time as well.

Post Harvest Primocane Disease Evaluations

Spur blight infection of primocanes was evaluated at each of the farms in August or September using field disease ratings and a more detailed count of the actual number of lesions on primocanes (Bristow data). Results are summarized below (Table 2). Disease ratings, performed during normal scouting indicated increased levels of infection in the Traditional vs IPM plot at one of the Whatcom farms and in the IPM vs Traditional plot at the Skagit site. In the second Whatcom farm site, there was no difference between the Traditional and IPM plots and disease incidence was low. Increased spur blight in Whatcom 1 in the Traditional plot is most probably due to the timing of liquid lime sulfur (Sulforix) in this plot compared to the IPM plot. Delaying this application (IPM strategy) may provide better control of the overwintering stage of spur blight, resulting in reduced disease severity after harvest. There were no other differences in the fungicide spray programs between these two plots. Increased spur blight in the IPM plot at the Skagit site is most likely due to the elimination of one Captan application (early May) in the IPM plot compared to the Traditional. At this site, Sulforix was applied at the standard timing (early March) in both plots. At the other Whatcom site (Whatcom 2), Sulforix was delayed in both the IPM and the Traditional plots. This delayed application (mid-April) has become standard practice for this grower based on his experience with this strategy the previous season in an on-farm research trial. In spite of an otherwise reduced fungicide program in the IPM vs Traditional plots on this farm (6 vs 8 applications), there was no obvious difference in spur blight between the two plots. This may be due to the benefits of the delayed Sulforix in both plots or that the frequency of summer fungicide application , though reduced in the IPM plot was still adequate for spur blight control, or both.

Field ratings from each site correlated well with the more precise counts conducted by Dr. Pete Bristow. The discrepancy between low field disease ratings and the relatively high lesion counts in both the IPM and Traditional plot at the Whatcom 2 site is explained by the one month delay between the field rating and the collection of primocanes for lesion counting at this field. This illustrates the progression of the disease during September. This level of infection (2-3 lesions per cane) is still quite low for this late in the season. Lesions were most commonly found 3 to 5 feet high on primocanes.

Table 2: Summary of Spur Blight (Didymella applanata) infection on primocanes.

* Rating of 0= no spur blight lesions on primocanes, 3=numerous spur blight lesions on primocanes

** Mean of four replicates per plot (Pete Bristow data)

Any problems or limitations?

Some of the cooperating growers’ "Traditional" spray programs were influenced by the ongoing dialogue between growers and researchers, which provided them with scouting information they otherwise would not have had. This makes it difficult to accurately measure the differences between the two strategies.

What did we learn?

Difficult to pin down either a "Traditional" or an "IPM" spray program because each is dynamic and reflects different sampling and decision-making inputs which can vary across farms and from year to year. In this project, the rigorous scouting and the exchange between growers and researchers resulted in balanced, knowledge-based decision making. This is the essence of IPM, and this ultimately separates an IPM approach from a more traditional approach.

This project has reinforced the major benefits of IPM scouting, which are reduced risk of crop damage from pests and improved timing of applications. Scouting highlights the variation in pest species and pressure from field to field. Cooperating growers found the scouting information to be extremely valuable as a more precise management tool.

Significant range in pesticide material costs from farm to farm, which is mostly influenced by frequency of fungicide applications and market destination of fruit. Pesticide inputs are lower when crop is destined for the juice market compared to the fresh market or higher end processing markets.

Root weevil species composition and density varies between fields. For most accurate results, sampling the canopy for adult weevils with a beating tray should be performed at night. Brigade, applied as a pre-harvest, basal spray provided good adult root weevil control.

The different leafroller complex in Skagit County necessitated different management strategies when compared to Whatcom County. In Skagit, well-timed Bt. applications targeting orange tortrix appear to be a much more important tactic, particularly with fresh market berries, when compared to Whatcom County.

Raspberry fruit which appears free of botrytis infection in the field can rapidly develop mold after harvest and threaten marketability, and confirmed resistance of Botrytis to key fungicides is a major problem facing the industry.

Where do we go from here?

Continue to improve scouting procedures, timing, and demonstration of techniques to growers so that they are more inclined to take an active role in scouting their own acreage.

Improve our understanding of spider mite injury levels and factors which influence their rapid development. This may include soil moisture, plant nutrition, nematodes, and other soilborne pests which cause plant stress.

Improve our understanding of nutritional factors and other cultural practices which may influence Botrytis fruit infection. Identify and pursue registration of fungicides with activity against Botrytis. Use this experience to support the development and use of resistance management techniques in the future.

Improve our knowledge of raspberry fruitworm biology, monitoring, and injury levels.

In general, attempt a more holistic/multidisciplinary approach to pest management in raspberries. We need to better understand how farming practices, as well as other seemingly unrelated biotic factors influence pest development. With this knowledge, farmers will be better prepared to avoid pest problems rather than just react to them once they have developed. Research projects should be designed to assist this effort.

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