March through September, 1999
Grower cooperators included Frank DeVries, Raj Bathe, and David Youngquist. WSU personnel included Dr. Pete Bristow (Plant Pathologist), Dr. Lynell Tanigoshi (Entomologist), and Geoff Menzies (WSU Lynden Research Station).
Paired 2-acre plots were selected on three farms; two in Whatcom County and one in Skagit County. These farm sites are referred to in this report as Site 1 or Site 2 in Whatcom County and Site 3 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 WSU Vancouver, Lynden Satellite 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 the plot were regularly sampled in each plot 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. 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. Sprays, when necessary were applied by cooperating growers with calibration assistance provided by WSU personnel. Spray records were kept for each farm and the cost of each program was estimated based on discussion with chemical suppliers (see Attachments).
Scouting was conducted between 15 and 20 times from late March through mid September on these farms, with an average of 16 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 5.3 visits prior to bloom (late March through mid-May), 5 visits during bloom and prior to harvest (late May through early July), 4 visits during harvest (early July through mid- August), and 2.3 visits after harvest (late August through mid-September).
Average root weevil larval density in the top 6 inches of soil in late March was 0.3 per square foot at Site 1, 7.0 per square foot at Site 2, and 1.5 per square foot at Site 3. The majority of these root weevils were black vine weevil, the key harvest-contaminating insect pest in raspberries. The first detection of the pupal stage in the soil was on April 30. First emergence from the soil of adult black vine weevil in Whatcom County was recorded on May 28. 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 early June (see Figure 1).
Figure 1: Black vine weevil lifestage distribution in the top 6 inches of soil, Whatcom County raspberry field on Birch Bay Lynden Road, 1999.
Early season bud damage from the April-emerging clay colored weevil was significant at Sites 2 and 3 necessitating mid-April basal applications of Brigade. Clay colored weevils in the raspberry canopy are sampled using a 16-inch square beating tray. The tray is held a foot below the top training wire, which is struck three times with a small club. Insects that fall to the tray are identified and counted. Ten tray samples are taken at each of four sites within each plot. Night sampling in mid-April at Site 2 revealed average populations of 9 to 14 weevils/10 trays in the traditional and IPM plots respectively. Comparisons made between daytime and evening sampling within the IPM plot at this site confirmed that detection during the day with this method is much less reliable than at night. This is particularly true at the early bud break stage when there is minimal cover for clay colored weevils during the day, which forces them to the ground during daylight hours. At Site 3, bud damage was noted during the daytime visit on April 12 but no weevils were detected with the beating tray. Nighttime sampling on April 15 revealed an average of 5 weevils /10 trays and 4 weevils/10 trays in the IPM and Traditional plots respectively. Had we not shared these scouting results with this grower, he would not have been aware of the damage clay colored weevils were doing in his field and he would not have sprayed. This pest was not detected at Site 1 with either day or nighttime sampling and therefore no treatment was necessary.
Using the beating tray, raspberry fruitworm was detected at only one of the three farms (Site 2). The first detection was on May 10, prior to any bloom. As bloom started to develop in late May, beating tray sampling revealed only one beetle in 40 trays in the IPM plot and no detections in 40 trays in the Traditional plot. Five minute bloom searches were also conducted to assist with detection of this insect. Using this method, 3 beetles were detected in the IPM plot and 7 beetles were detected in the Traditional plot. At this same visit in late May, beating tray samples revealed significant numbers of clay colored weevil in the canopy during the afternoon even with temperatures approaching 80F. An average of 5 to 6.5 clay colored weevils/ 10 trays were detected in both plots, in spite of the mid-April basal Brigade application which provided good initial control. This resurgence of clay colored weevils was likely due to ongoing emergence of adult weevils from the soil after the residue of the mid-April Brigade had broken down. In late May, the IPM plot was treated with a full canopy Guthion spray and the Traditional plot was treated with a full canopy Diazinon spray, which is the industry standard for pre-bloom fruitworm control. Follow-up sampling one week after treatment at night and during the day showed excellent control of clay weevils and fruitworm with Guthion in the IPM plot. In the Traditional plot, Diazinon controlled fruitworm well, but clay weevil counts averaged 2 /10 trays during the day and 6/10 trays at night indicating marginal control compared to Guthion. Table 1 shows clay colored weevil sampling results from bud break through the bloom period just prior to harvest at Site 2 in Whatcom County.
Table 1. Clay Colored Weevil Sampling at Whatcom Site 2
|
Average Number of Clay Colored Weevils/10 Trays |
|||
|
Sampling Date |
Day or Night |
Traditional |
IPM |
|
April 14 |
Night |
9.0 |
13.7 |
|
April 20 |
Night |
0.7 |
0.8 |
|
April 30 |
Day |
1.3 |
0.0 |
|
May 10 |
Day |
1.7 |
1.5 |
|
May 12 |
Night |
NS |
3.0 |
|
May 24 |
Day |
5.0 |
6.5 |
|
June 2 |
Night |
6.0 |
0.3 |
|
June 4 |
Day |
2.0 |
0.0 |
|
June 29 |
Day |
1.0 |
0.3 |
Traditional plot sprayed on April 15 with basal Brigade and on May 25 with full canopy Diazinon.
IPM plot sprayed on April 17 with basal Brigade and on May 25 with full canopy Guthion
Fruitworm treatment was not required at Sites 1 and 3, and beating tray sampling during late May and June detected very low levels of clay weevils at Site 3 only. Therefore, a second spray prior to harvest targeting clay weevil was not necessary at Site 3, probably due to the lower initial population at this site.
Adult black vine weevils were first detected with beating tray samples at all sites in late June just prior to the start of harvest. Although sampling indicated fairly low populations (range of 1-3 weevils/40 trays) at this time, both Sites 1 and 2 in Whatcom County were treated with a pre-harvest Brigade "cleanup" spray. These fields are machine-harvested and both growers were picking into flats for high-end markets which also have low tolerance for insect contaminants. Post-treatment scouting documented good control of all insect pests present including weevils, lygus bugs, earwigs, as well as destruction of the most common beneficial insects, lady beetles and lacewings. Raspberry aphid populations increased during harvest approaching 200 aphids/10 trays and 150 aphids /10 trays respectively in Sites 1 and 2 by late August. In spite of these apparent high densities, neither grower experienced fruit contamination problems from this insect.
Adult black vine weevils were detected in early July at site 3 in Skagit County. Through the first two weeks in July counts did not exceed 1 weevil/40 trays. Since this field is hand-picked for the fresh market, which greatly reduces the likelihood for insect contamination of fruit, the grower elected not to apply a pre-harvest "cleanup" Brigade spray in either the IPM or Traditional plots. Raspberry aphid populations never increased significantly at this site. However, a mix of several root weevil species including black vine, clay colored, and obscure were detected during late July and through mid-August. Total counts reached 9-13 weevils/40 trays at this time. Considering this as well as an increasing twospotted spider mite population, Brigade was applied immediately after harvest to control both pests in both the Traditional and IPM plots.
Obliquebanded leafrollers (OBLR), the most common leafroller found in Whatcom County was not detected in pheromone traps in either of the Whatcom sites. With routine examination of new fruiting lateral shoots in late April and May and primocane tips in June through mid-August, larvae were found in late August at a very low level of infestation (1.2% of hills infested) in the Traditional plot at Site 2 only. The recommended threshold for this insect when found prior to or during harvest is 10% infestation of hills. Pre-harvest Brigade sprays applied in both of these sites may have contributed to the low numbers detected at these sites. In late June, a low infestation (1.2% infested hills) of bertha armyworms was detected in the IPM plot at Site 1. This insect was not detected again following the Brigade "cleanup" spray in this field.
OBLR activity was extremely low at Site 3 in Skagit County as well, with no larvae detected in either fruiting lateral shoots in the spring or primocane tips during the summer. OBLR moths were detected in pheromone traps only once during mid-August. The dominant leafroller on raspberries in Skagit County is the orange tortrix. Moths were not detected until mid-May. This was very delayed compared to the previous year and was likely due to the unusually cold weather in April. Trap catch remained relatively low for this pest through mid-June, and then peaked in late June at 160 moths per trap. Flight activity dropped off until early August and then began to increase again. Orange tortrix larvae were detected in primocane tips about three weeks after peak trap catch in the IPM plot, but the degree of infestation (4% infested hills) was in itself below the treatment threshold (see Figure 2).
Figure 2: Orange tortrix flight and primocane infestation
However, in 11% of the hills, primocanes were infested with bertha armyworm larvae at this same time in mid-July. Both of these caterpillars can contaminate hand-picked fruit. This prompted Bacillis thuringiensis applications in both the IPM and Traditional plots. Three applications of Condor were applied in the Traditional plot and just a single application of MVPII (microencapsulated Bt.) was applied in the IPM plot. Both tactics provided good control of these pests as shown below in Figures 3 and 4.
Figure 3: Primocane infestation in IPM plot
Figure 4: Primocane infestation in Traditional plot
As we have observed in the past, spider mite dynamics and interaction with predatory mites are highly variable from field to field. Whatcom Site 1 has a recent history of yellow spider mite infestation typically requiring control just prior to the onset of harvest. However, the population never reached a density requiring control this season in either the IPM or Traditional plots. Yellow mite levels increased significantly after harvest, particularly in the Traditional plot, but for this late in the season and with a strong response from the predatory mite, Amblyseius fallacis, there was not enough feeding damage to warrant control. An action threshold has not been established for this pest in raspberries, but the plants appear to tolerate much higher densities of yellow mites compared to twospotted mites. The critical period for spider mite control is from June through August. The ratio of predatory mites to prey was most favorable in the IPM plot but significant in both, particularly in early September (see figures 5 and 6).
Figure 5: Mite populations at Site 1
Figure 6: Predatory:prey ratio at Site 1
In Whatcom Site 2, yellow spider mites were again the dominant species but they never approached economic levels in either the Traditional or IPM plots. Predatory mite activity was very low in this field all season, showing a slight increase in late August. Past research has suggested that spider mite flare-ups in raspberries in western Washington can be associated with more frequent insecticide use. In spite of three pre-harvest insecticide applications in this field, no such flare-up occurred.
In the Skagit county Site 3, Twospotted spider mites increased rapidly towards the end of the harvest period, particularly in the IPM plot. The predator to prey ratio was more favorable for spider mite suppression in the Traditional plot compared to the IPM plot during the harvest period. Brigade was applied immediately after harvest to control root weevils and spider mites in both of the plots. Figures 7and 8 below show these population trends and predator to prey ratios. It is interesting that this site had a reduced insecticide program with only one basal Brigade application in late April and no "cleanup" Brigade spray and yet still experienced a rapid increase in twospotted mites in the IPM plot. The August 19 Brigade provided excellent spider mite control with apparently minimal impact to pedatory mites. The predatory mite population dropped off rapidly in mid-September due most likely to absence of prey and subsequent predator starvation.
Figure 7: Mite populations at Site 3
Figure 8: Predatory:prey ratio at Site 3
In early April, fruiting canes were examined and rated (scale of 0-3) for spur blight, cane blight, and cane botrytis. Results are shown in Table 2 below. Primocanes were rated in the late summer for spur blight and cane botrytis. In this qualitative rating, 0=no detection and 3=widespread/severe disease incidence.
At Site 1, the higher April spur blight rating in the Traditional plot compared to the IPM plot supports the late summer observations in these two plots from the previous season. At that time the Traditional plot had an average of 35 lesions per 20 primocanes compared to 13 lesions per 20 primocanes in the IPM plot. This reduced incidence of spur blight infection in the IPM plot was attributed to a delayed Sulforix application the previous spring. There was no significant difference between the cane disease fungicide programs in the Traditional and IPM plots during the 1999 season in this site. No cane blight was detected in this field and cane botrytis levels were very low.
Based on the April ratings, Site 2 had the the highest carryover of both spur blight and cane blight. Had the summer readings been taken later in September, the spur blight ratings in both plots would likely have been higher as current season primocane infection can be late in developing. A mid-May Captan application was advised in the IPM plot to help suppress spur blight. Benlate was also advised after harvest as this is the ideal material to control cane blight. The fungicide cost was actually higher in the IPM plot compared to the Traditional because disease pressure was high in this field which warranted a fairly rigorous spray program. Most of the increased cost was due to 3 applications of Switch in the IPM plot compared to the reduced 2 applications of Switch in the Traditional plot. Cane botrytis levels were low in both plots, most likely because this is an older, low-vigor field and the fungicide programs controlled Botrytis.
Cane disease levels were generally quite low in both plots in Site 3. No cane blight was detected. Spur blight ratings in September were slightly higher in the IPM vs the Traditional plot but because disease incidence is very low anyway, this difference is probably insignificant in terms of damage to the planting. Five fungicide sprays targeting Botrytis were applied in the Traditional plot compared to three in the IPM plot. The two extra sprays were applied during the harvest period at an additional cost of about $100/acre. There was no apparent benefit of this more intensive program. Cane Botrytis levels were very low in both plots.
Table 2. Spring and late summer cane disease ratings (scale of 0-3)
|
Location |
Sample Date |
Traditional |
IPM |
||||
|
Spur Blight |
Cane Botrytis |
Cane Blight |
Spur Blight |
Cane Botrytis |
Cane Blight |
||
|
Site 1 |
April 29 |
2.70 |
0.00 |
0.00 |
1.50 |
0.25 |
0.00 |
|
Sept. 13 |
1.75 |
0.50 |
NA |
1.00 |
0.00 |
NA |
|
|
Site 2 |
April 29 |
3.00 |
0.00 |
1.50 |
2.50 |
0.00 |
1.50 |
|
Aug. 3 |
0.75 |
0.00 |
NA |
0.00 |
0.00 |
NA |
|
|
Site 3 |
April 22 |
1.25 |
0.75 |
0.00 |
1.25 |
1.00 |
0.00 |
|
Sept. 14 |
0.50 |
0.00 |
NA |
1.25 |
0.25 |
NA |
|
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 last year, this disease caused reduced fruit quality and forced each grower out of their intended markets and into lower value and lower net return markets. Quality problems were largely due to weather patterns favorable for fruit infection and spread as well as widespread resistance to the most commonly used eradicant fungicides, Rovral and Ronilan. For this reason, emergency registration for the 1999 growing season was acquired for an alternative, eradicant fungicide called Switch. This material was heavily relied upon for fruit rot control during the 1999 season. Raspberry fruit was collected on two occasions from both the Traditional and IPM plots from each site and evaluated for fruit rot infection. The results are presented below in Tables 3 and 4 for both fresh and processed handled berries:
Table 3. Fresh market fruit rot test
|
Location |
Harvest Date |
Percentage Fruit Rot |
|
|
Traditional |
IPM |
||
|
Site 1 |
July 22 |
5.7 |
18.4 |
|
August 2 |
31.2 |
44.5 |
|
|
Site 2 |
July 22 |
22.3 |
59.3 |
|
August 2 |
48.9 |
52.1 |
|
|
Site 3 |
August 2 |
9.9 |
10.9 |
|
August 11 |
32.7 |
39.2 |
|
Berries harvested at the pink stage of ripeness. Held for one day at 32F, one day at 40F, and four days at 58F. These conditions are thought to mimic conditions experienced by fresh fruit in normal marketing channels
Table 4. Processed market fruit rot test
|
Location |
Harvest Date |
Percentage Fruit Rot |
|
|
Traditional |
IPM |
||
|
Site 1 |
July 22 |
10.9 |
17.2 |
|
August 2 |
98.4 |
97.4 |
|
|
Site 2 |
July 22 |
46.4 |
70.3 |
|
August 2 |
99.5 |
100.0 |
|
|
Site 3 |
August 2 |
86.5 |
89.1 |
|
August 11 |
72.9 |
67.2 |
|
Berries harvested when fully ripe. Placed individually on moist newspaper and incubated at 100% relative humidity for three days at 58F
In the fresh market test, the percentage of fruit rot was consistently higher in the IPM compared to the Traditional plots at all sites. However, none of the differences were statistically significant. There were also no statistically significant differences between the IPM and Traditional plots in the processed market tests. Botrytis fruit rot was well controlled in each of the sites and in both the IPM and Traditional control programs. In general, three well-timed applications of Switch combined with one application of Rovral plus Captan during the bloom period (the IPM approach) provided excellent fruit rot control during the 1999 season. Tank mixing Captan with Switch or a fourth application of Switch did not appear to offer any significant benefits compared to the IPM program.
Decision making in the IPM plots was based upon discussion of field data, grower experience and pest tolerance, intended markets, and input from researchers. In general, this project confirmed the variation that exists from farm to farm regarding pest density and pest species and therefore spray needs and timing. This type of information is only learned through regular and systematic scouting. 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 plots. On average, the pesticide cost was reduced by $54/acre in the IPM plots when compared to the traditional plots. Cooperating growers were privy to scouting results and involved in decision-making in the IPM plots. This influenced their spray program in the adjoining Traditional plots to varying degrees. This project design admittedly may blur the distinctions between the two approaches, but is hard to avoid with an on-farm research and education project such as this in which the grower is expected to play an active role. The spray records for each site are included in "Attachments A, B and C ".
Table 5. Traditional versus IPM program pesticide costs
|
Traditional |
IPM |
|||||
|
Fungicide |
Insecticides |
Total |
Fungicide |
Insecticide |
Total |
|
|
Site 1 |
296.63 a |
52.00 |
348.63 |
203.05 |
52.00 |
255.05 |
|
Site 2 |
171.60 |
85.50 |
257.10 |
215.37 b |
88.20 |
303.57 |
|
Site 3 |
275.59 c |
96.59 d |
372.18 |
174.94 |
81.40 |
256.34 |
|
Average |
247.94 |
78.03 |
325.97 |
197.78 |
73.86 |
271.65 |
Notes
This project has shown for the second season that there is significant variability in pest complex and intensity from one site or field to the next. This knowledge which is only acquired through routine field scouting can be used to influence selection and timing of pesticide applications. Early season scouting for clay colored weevils and their damage during bud break and into the early bloom period is very important. Related research has shown that this pest, when numerous can reduce yield by 25%. Sampling with a beating tray is straight forward and not very time consuming, but should be done at night during bud break for best results. Due to the extended period of adult clay weevil emergence from the soil, two insecticide applications may be required to control this pest (bud break period and 3 weeks later, prior to bloom).
Black vine weevil development in the soil this season was initially delayed compared to the previous year. However, there was a rapid transformation from the pupa to adult stage in late May and early June this season. Pre-harvest Brigade sprays again appeared well-timed to control summer–emerging adults prior to the onset of egg laying. An early season strategy should be developed to control overwintering adults which begin laying eggs long before the start of harvest.
Beating tray sampling during the harvest period revealed that raspberry aphids migrate into Brigade-treated fields and feed on new growth which has no insecticide residue. Although aphid populations increased significantly in two of the three sites, growers in this project experienced no fruit contamination problems and did not have to treat this pest. However, many other growers found it necessary to treat this pest during the harvest period to avoid fruit contamination. Pre-harvest Brigade treatments again did not appear to induce spider mite flare-ups in this project. When used after harvest at one site, Brigade provided rapid and sustained control of spider mites with minimal disruption of predatory mites.
The combination of pheromone trapping and field scouting for leafroller larvae showed minimal pest presence in Whatcom County and delayed orange tortrix flight in Skagit County during 1999 compared to 1998. One application of Bacillus thuringiensis about 3 weeks after peak flight of orange tortrix controlled this pest and the more numerous bertha armyworm larvae, which also feeds on primocane tips at that time.
Cane disease ratings conducted during the bud break period provide the opportunity to roughly categorize the carryover of spur blight and potential for disease and to determine the presence or absence of cane blight. Cane blight if present is the more serious disease and can drastically reduce plant vigor and current season yield due to the damage it causes to floricane vascular tissue. Where cane blight is detected, and depending on weather during and after harvest, cultural practices and a fungicide application targeting this disease should be considered.
Fruit rot caused by Botrytis, the most important pest during the previous two seasons, was well controlled this year with three applications of Switch plus one application using other materials (Rovral plus Captan) from early bloom to the start of harvest. Sprays were applied at approximately 14-day intervals from early June through the first week in July.
IPM scouting in raspberries is important because it helps the raspberry grower identify and manage risks to the crop posed by key pests. Pest development, presence, and intensity varies between fields and from one year to the next. Regular field scouting as performed in this project and described in the manual, Integrated Pest Management for Raspberries, a publication of WSU Whatcom County Cooperative Extension, provides raspberry growers with the time-critical and field-specific information necessary to optimize their pest management program.