Arthropod Management in California Blueberries David Haviland and Stephanie Rill UC Cooperative Extension, Kern Co. Blueberry Field Day 20 May 2009
Citrus thrips White grubs Flower thrips Flatheaded borer
Pacific Flatheaded Borer Adults emerge April-July Lay eggs on bark Usually weak or sunburned areas Feed within wood One generation per year Management = pruning it out after harvest
Flower thrips Migrate from foothills and pastures when host plants dry down Attracted to flowers Can be found in very high numbers in blueberries Can cause halo spot from oviposition Damage is rare Not very noticeable unless actively searching
Citrus thrips vs. Flower thrips Yellow, have waists, on new flush, very active, present all summer Yellow/black, long and slender, on flowers, sluggish, present at bloom
Citrus thrips Overwinter as eggs in leaves, found in canopy starting in June (3 rd generation) Not usually an issue until after harvest Populations fluctuate June through October 900 18 Mean no. of thrips per trap 800 700 600 500 400 300 200 100 16 14 12 10 8 6 4 2 Mean no. of thrips per beat sample 0 0 15-Jan 4-Feb 24-Feb 16-Mar 5-Apr 25-Apr 15-May 4-Jun 24-Jun 14-Jul 3-Aug 23-Aug 12-Sep 2-Oct 22-Oct 11-Nov 1-Dec 21-Dec 2006 Traps 2007 Traps 2006 Beats 2007 Beats
Damage to blueberries During harvest they are found on the suckers and not near the fruit (1 st & 2 nd generation) Feed on new flush all summer Shoot stunting Leaf deformation Shortened internodes Stem scarring Varies by variety
Damage to blueberries
Thrips and New Growth Increased thrips = decreased new green flush growth 25 Average shoot length (cm) 20 15 10 5 0 2006 Misty y = -0.6596x + 24.472 R 2 = 0.8083 2007 Star y = -0.1586x + 5.9812 R 2 = 0.5129 0 5 10 15 20 25 30 35 Average thrips per beat sample 2006 2007 Linear (2006) Linear (2007)
Yield Studies Summary Impact Reduced growth (2 yrs) Reduced number of berries (1 yr) Reduced yield per plant (1 yr) No impact Size of berries Quality of berries Shift in harvest date Average yield per plant (lb, May-June 2007) Average yield per plant (lb, May-June 2007) 20 18 16 14 12 y = 0.2461x + 11.464 R 2 = 0.7687 10 8 10 12 14 16 18 20 22 24 20 18 16 14 12 shoot growth in August 2006 (cm) y = -0.0906x + 17.192 R 2 = 0.7902 10 0 5 10 15 20 25 30 35 40 average thrips per beat sample (August 2006)
Control methods Cultural controls Avoid more susceptible varieties Overhead irrigation High pressure water Biological controls Predators and parasites unavailable or unaffective Beauveria shown to have limited results Chemical controls Rotation of insecticide sprays
Cultural controls- avoid Star 16 Average citrus thrips per beat 12 8 4 19-Jun 25-Aug 0 Jubilee Misty O'Neal Star Variety Mechanism of selectivity not known.
Lacewing & High Pressure Water 2008 (2 trt/week for 5 weeks @ 75GPA) 90 80 Average thrips per beat sample 70 60 50 40 30 20 10 0 18-Jul 20-Jul 22-Jul 24-Jul 26-Jul 28-Jul 30-Jul 1-Aug 3-Aug 5-Aug 7-Aug Lacewing Jewel Water Jewel Control Jewel Lacewing Emerald Water Emerald Control Emerald 9-Aug 11-Aug
Beauveria and sprinklers Evaluated Overhead irrigation Thrips don t t like water Beauveria Mycotrol Millet seed dispersal Results Major benefit of sprinklers Not likely due to affect on thrips Beauveria didn t t do much length of new green flush (cm) Avg thrips per beat sample 40 35 30 25 20 15 10 5 0 7/25 8/1 8/8 8/15 8/22 8/29 14 12 10 8 6 4 2 0 shoot8/19 shoot8/29 shoot9/4 MINW MIYW MYNW MYYW NBNW NBYW MINW MIYW MYNW MYYW NBNW NBYW
Treatment Thresholds Do not have to worry until harvest is over Monitor, treat about 20 thrips per beat sample When damage is visible on the plants
Insecticide Studies 2006-2008 2008 Products that work Success/Delegate/Entrust (organic) spinosad Products that work moderately Assail, Danitol (if not used repeatedly) Products that might work Lannate/Diazinon the first time Products that do not work Oils, soaps, pyrethrin/pyrethroids such as Evergreen, Pyganic, Neem-Oils
White Grubs (Chafers) May beetle, scarab, chafer, white grub, June bug, etc. C-shaped grub Brown adult Native to California Highly polyphagus on broadleaves Pest of turf, sweet potatoes, and blueberries
Beetles captured in light trap
Estimates of life cycle (based on info on masked chafer in lawns and Japanese beetle on east coast) One generation per year Adults in June Eggs- mid to late June Grubs- hatch in July most are likely fully grown 3 rd instar by the fall Overwinter Pupae- mid May to mid June Adults in June
Why a pest of blueberries? To a grub, a blueberry field probably looks and feels like a lawn Lots of organic material (soil amendments) Thick thatch layer (mulches) Fine, shallow roots Consistent moisture In fact, grubs often show up in the blueberry field before the plants Can stunt and kill young plants Populations build over time
Management in turf Insecticides Imidacloprid (Admire) Timing likely best in ~early July when grubs are small Not likely effective in blueberries due to soil binding Biological Control Nematodes Heterorhabditis bacteriophora A hunter/searcher Commercially available, applied through the drip line Organic Other pathogens such as milky spore Not available in California
Nematode trial (exploratory quick and dirty) Applied April 1, 2009 Commercial rate Commercial blueberry field Koppert Biological Systems, Inc. Chrissie Davis, cooperator Sentinel grubs evaluated 5 weeks later 25% of the grubs missing 25% sick 6% confirmed by nematodes
Prognosis? Nematodes have promise Can be delivered through drip system Can seek out and infect grubs But Optimal timing unknown Rates needed unknown Effects on mortality unknown Effects on fecundity unknown Secondary infection unknown Affects on feeding unknown Damage prevention unknown