2006 Blueberry Agricultural Research Grant Proposal

Seasonal Life-history and Management Strategies for Blueberry Gall Midge and Thrips in Highbush Blueberry

Cesar Rodriguez-Saona Extension Specialist in Entomology Rutgers Cooperative Research & Extension P.E. Marucci Blueberry/Cranberry Research & Extension Center Chatsworth, NJ 08019

After the Food Quality Protection Act (FQPA) was implemented in 1996, several broad-spectrum organophosphate and carbamate insecticides have been under review, scheduled for cancellation, or severely restricted for use in blueberries due to health and environmental concerns. Limitations in the use of broad-spectrum insecticides have led to an increase in insect pests previously considered secondary or minor. For example, since implementation of the FQPA, there has been a steady increase in the abundance of thrips and blueberry gall midge populations in NJ blueberry farms. In a recent survey conducted at the Rutgers Research Center, blueberry growers in NJ ranked thrips and blueberry gall midge among the six most important pests in their farms.

This study was conducted to determine the seasonal fluctuations of thrips and blueberry gall midge populations in highbush blueberries and to evaluate new reduced-risk insecticides for control of these insect pests. Information on the distribution of thrips in highbush blueberries and a better understanding on the phenology of blueberry gall midge are a pre-requisite to the development of chemical control strategies. This study will likely provide insights on when, where, and what to apply for thrips and blueberry gall midge control.

Thrips: Several species of thrips have been reported to infest highbush blueberries in NJ. These were recently identified to include at least two species: Frankliniella tritici and Scirtothrips ruthveni. Thrips injury in blueberries can be recognized by tight curling of leaves, accompanied by malformation of leaves. In addition to injury to leaves, and more importantly, some of these thrips species preferentially feed on flowers. This feeding injury to flowers can affect fertilization and subsequent fruit set. Damage to ovule has also been reported, and under severe conditions, small berries drop prematurely causing direct yield loss. Dimpling on the fruit has been noticed if the infestations are severe. As much as 60% reduction in fruit set has been attributed to thrips injury in Southern highbush blueberries in Georgia and Mississippi (Horton and Samson 2001).

Previous studies conducted at Rutgers Research Center by Dr. S. Polavarapu (unpublished data) showed that white sticky traps are more suitable for thrips population monitoring than yellow or blue in highbush blueberries. However, these studies were unable to explain the high variability observed from week to week among three sampling methods: white sticky traps, beating trays, and leaf analyses. Because the distribution of thrips species can be uneven on a plant, with niche specialization based on height (low versus high) (Irwin et al. 1979), this study expanded the previous studies to determine the within-plant distribution of thrips, in order to help clarify the observed seasonal differences between sampling methods. From the 1st week of April until the last week of August, the population of thrips was monitored in eight randomly selected blueberry bushes. White sticky traps were placed within each bush at three heights (low, medium, and high). From bud formation/elongation until flowering, five flower and leaf buds were collected weekly from each height and examined for thrips. During flowering, five flower clusters were collected at each height per bush. From fruit maturation until harvest, five fruit clusters were collected weekly per height/bush. In addition, leaf samples were collected weekly from bloom until the end of August from five terminals per bush at each height. Buds, flower, leaf, and fruit samples were taken from 8 randomly selected bushes around each sticky trap. Six reduced-risk insecticides were compared for efficacy in controlling thrips in a blueberry field at the P.E. Marucci Center. One registered reduced-risk compound (SpinTor) for thrips control was compared to five new unregistered reduced-risk insecticides.

Figure 1. Phenology and Trap Height on Abundance of Blueberry Thrips The highest numbers of thrips were found in the “high” sticky traps 800 Low while the lowest numbers were found in Medium

p High a the “low” traps (Figure 1). Abundance r 600 T

of thrips in sticky traps peaked soon p

after flowering. In contrast, the highest r h 400 T

numbers of thrips in bushes were found f o

in “low” leaves also following fruit set b m u 200

(Figure 2). Only few thrips were found N in flower and leaf buds, flowers, and fruit. SpinTor and three other reduced- 0 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

risk insecticides were effective at 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 / / / / / / / / / / / / / / / / / / / / / / 6 3 0 7 4 1 8 5 1 8 5 2 9 6 3 0 7 3 0 7 4 1 / / / / / / 1 2 2 1 1 2 1 2 2 1 2 2 1 1 2 3 / / / / / / / / / / 4 / 5 / 6 6 / 7 / / 8 / reducing thrips populations (Figure 3; Plant Phenology 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 8 Bars with different letters indicate Flower Bud Flower significant differences between Fruit treatments, P  0.05).

Figure 2. Phenology and Height on Abundance of Blueberry Thrips

50 Low Vegetative Medium 40 High Figure 3. Efficacy Trial of Reduced-Risk Insecticides on Blueberry Thrips

30 b s l s 20 a p i n r

i 25 h m r T 10

T 20 o

0 r a 1 e 0 / a b E 15 S

m 50 ± u

s N Reproductive 10 p i ac 40 r h c

30 N 0

20 Control Spintor A B C D E F

0 Bud Flowering Fruit Set- Post- Elongation Maturation Harvest Blueberry Gall Midge. Blueberry gall midge, Dasineura oxycoccana (also known as cranberry tipworm), is becoming a concern to NJ blueberry growers due to an increase in population size. This insect is considered a major pest in the Southeastern US, where untreated populations are capable of destroying up to 80% of the floral buds (Lyrene and Payne 1992). Blueberries and cranberries are the only known host for blueberry gall midge. Females oviposit between the developing floral and vegetative bud scales. Newly hatched larvae feed on the innermost meristematic tissues, potentially reducing flower production and fruit yield.

Figure 4. Phenology on Abundance of Cranberry Tipworm Infested Tips From the 1st week of April until

40 the last week of August, the number of Edge

E Interior infested terminals by blueberry gall S ±

s p midge larvae was monitored in 6 i 30 T

blueberry farms from 20 randomly e g a

selected bushes (10 from the edge and m

a 20 D

10 from the interior of each farm). Ten f o

terminals were sampled from the lower b

m 10 1/3 of each bush. A test was conducted u N in a commercial blueberry field to compare the efficacy of six reduced-risk 0 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 / / / / / / / / / / / / / / / / / / / / / / 3 0 7 1 8 5 1 5 2 9 3 0 7 0 7 4 1 6 4 8 6 3 / / / / / / 2 1 1 2 1 2 1 1 2 1 2 2 2 1 2 3 / / / / / / / 4 / / 5 / / 6 6 / 7 / 8 / / /

insecticides in controlling blueberry gall 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 8 midge. The same insecticides tested Plant Phenology Flower Bud against thrips were used in the blueberry Flower gall midge test. Fruit

Number of damaged tips peaked from the last week of June until the last week of July (Figure 4). There were no differences between numbers of Figure 5. Efficacy Trial of Reduced-Risk Insecticides on Cranberry Tipworm damaged tips in edge compared to

a a interior bushes, indicating that insect n i a a m r

damage to terminals might be caused e T ab 0

by resident populations. Efficacy trials 1 / 6 ab ab E b showed that 2 reduced-risk insecticides S ±

were most effective at controlling p i T

blueberry gall midge populations d 3 e g (Figure 5). a m a D

N 0 References: Control Spintor A B C D E F

Horton, D. L. and B. Samson. 2001. Application for specific exemption (Section 18) for use of SpinTor 2SC on two blueberry pests (blueberry gall midge and thrips) in Georgia for the 2001 use season. Petition submitted to US EPA, March 2001. 7 p. Irwin, N.E.E., Yeargan, K.V., and Marson, N.L. 1979. Spatial and seasonal patterns of phytophagous thrips in soybean fields with comments on sampling techniques. Environmental Entomology 8: 131-140. Lyrene, P.M. and Payne J.A.. 1992. Blueberry gall midge: A new pest of rabbiteye blueberry in Florida. Proc. Fla. State Hort. Soc. 105: 297-300.