Rhagoletis completa
Walnuts have entranced societies for one thousand of years with their ravisher and shade – not to observe their delectable and extremely healthy nuts and worthful wood .
However , there is a disconsolate side to arise walnuts , and it comes in the form of a 1/4 inch foresighted louse – the walnut husk fly ( Rhagoletis completa ) .
This is the most vulgar pest encountered in both backyard and commercial-grade groves of walnut tree on the West Coast – and a serious problem for growers .
The larva of the walnut husk fly (Rhagoletis completa). Photo by Whitney Cranshaw, Colorado State University, Bugwood.orgvia CC 3.0.
Technically , it ’s the maggots that are the problem . They feed on the shuck that surrounds the ball .
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The severity of the damage count on when the larvae provender . It can range from the discolouration of the shell to the end of the kernel .
Even worse , the nub may grow mold . You may think of mold as just unpleasant , but this kind of fungus produces a dangerous carcinogencalled aflatoxin .
And the walnut husk rainfly is becoming an even more serious job by showing up much earlier in the time of year than normal – before the growers are ready for it .
We at Gardener ’s Path will take the air you through the step to monitor and protect your walnut tree tree – and when you will ask to hire a professional gadfly control expert .
What You Will Learn
Identification, Life Cycle and Distribution
The walnut tree husk fly ( WHF ) looks so striking that it is wanton to describe . It is the size of a housefly but chocolate-brown with a yellow semicircle on its back . And then there are its unique translucent wings – with heavy brownish - sinister band on them .
grownup come out from the soil from May to early fall and mate within 1 - 2 weeks . The females then lay eggs just below the walnut husk ’s Earth’s surface .
The larvae hatch into white maggots in 5 - 7 days , and problem really begins !
These 1/2 - in maggot feed on the shape of the husk . The larvae become scandalmongering with sinister mouthpart as they grow .
As they eat , the process loose the pigment in the walnut . This compound goes on to maculate the shell and change the flavor of the core .
bad - case scenario – the stalk stick around to the shells . This can guide to withered and moldy essence .
finally these infested walnuts pass to the earth , and the maggots burrow into the grease and pupate for 1 - 2 age .
Unfortunately , the soil hold back these pupae good from the element – and also most predators .
WHF are aboriginal to the southern and primal US but spread to the west in the 1920s . presently , they are a serious problem in California and Washington State where the bulk of US English walnut prodcution occurs .
Originally a quarantine pest in Europe , the flies became naturalise in southern Europe in the former 1990s .
Susceptible Walnut Species and Cultivars
preferent hosts for the WHF includeblack walnutsand all cultivar of English walnut .
peculiarly susceptible English walnut cultivars include Franquette , Hartley , Serr , and Tulare .
It can be authoritative to recognise what cultivar you are growing because some cultivars incur harm earlier in the season than others .
For example , the tent-fly attack the Hartley , Payne , and Serr cultivars in the first place than Chandler .
The Walnut Husk Fly is Spreading!
University of California , Berkeley Emeritus Professor and walnut husk fly ball expert Bob Van Steenwyktold GrowingProduce.comthat the pest is becoming a problem in new area .
In the Sacramento Valley in California , June 1 used to be when you would put your first trap out .
Now the pestsare arriving earlier in the season – possibly due to the warming of the climate . So you may require to start pin as early as May 1 in the lucky United States Department of State .
Effects on Walnuts
The symptoms of this infestation vary count on when the larvae attack the chaff .
If the infestation are early in the season , the nuts will still be develop . So the kernels themselves get damage , and there is the potential difference for you to lose your whole craw .
Early infestations are much more likely to give rise the toxic mildew ontogenesis along with sear and darkened nitty-gritty .
later on infestations maculate the carapace . The walnut stain wo n’t discolourise out well , so you wo n’t be able to betray your walnut in - shell .
However , at least the nub will retain its timber , so if you are uprise walnut to eat , you should be good to go .
The trouble may be that it may be difficult to remove the Isaac Hull .
However , you may get around that by putting the fruitcake in a damp gunny bag for several day . It should be easier to remove the Cordell Hull after that .
How to Monitor Adult Walnut Husk Flies
Unfortunately , since the nut and larvae are hidden within the husk , they are protect from insecticides .
You have to focalize your monitoring efforts on the grownup , since they are the central stage to control .
There is only a short time window to detect the adults before they start put down eggs .
Once the eggs have been laid within the husk , the larvae will acquire where you may not extend to them .
The size of mature walnut trees can make it difficult for homeowners to supervise and control walnut husk flies . It is not unheard of for residential walnut tree trees to be 120 feet tall !
treat a tree that size of it will pose problems with pesticide drift . So if you have a gravid tree , you should consult with a licensed master .
However , if you have a tree that is 10 - base tall or smaller , you could carry out all these tone yourself .
You may be familiar with yellowed sticky traps . That is what you may use to look for grownup tent-fly .
According tothe University of Californis Integrated Pest Management Program , you will want to get unbaited lily-livered muggy traps design forapple maggots(Pherocon AM NB ) that have been exceedingly - charge with ammonium carbonate to attract the adult flies .
What is Integrated Pest Management ?
IPM is an ecosystem - focussed style of direction that take into account you to manage your pests more sustainably , serve you to habituate less harmful pesticide whilst birth the added bonus of helping you to get to make out our gardens more closely .
Click here to determine more !
Do not use Malus pumila maggot traps that already contain bait because they will not pull the WHF .
Ideally , you should put the trap in the upper half of the canopy on the magnetic north side of the Sir Herbert Beerbohm Tree and at least six feet off the soil .
Monitor your traps at least twice a week and sooner more frequently .
You want to detect the adults ASAP , so you could kill them before they start lay the eggs that produce the menacing larvae .
Remove the rainfly and put them on a moody background signal .
Look for females – they are the ones with the yellow front leg . ( you may see this with a 10X hand lens system . )
Then arrest if the female is carrying eggs by mildly squeezing her abdomen . The eggs wait like small grain of Sir Tim Rice .
Even if you did n’t detect any fly in the former twelvemonth , you should keep monitoring because they can live in the soil for two years .
Or they may get along from your neighbor ’s tree ! Share and share alike .
Control
You will have to apply some sort of insecticide to master these pests and protect your walnut .
A unfit infestation could cause you to lose your entire craw of in - shell nuts . They will be worthless if they are not shelled .
If you grow a shelled cultivar , you could lose half the time value of your crop .
It is critical that you apply an insecticide ASAP after notice eggs .
Unfortunately , you will need to keep spraying until 1 - 2 weeks before the hulls break up .
Organic Insecticide/Bait
you may buy the organically certified production GF-120 that contains the natural insecticide spinosad along with come-on that attracts the flies .
GF-120 is as effective as traditional insecticides , but it does n’t cause the distinctive negative effects of aphids or mites flare up .
However , you do have to apply it in the beginning than conventional insecticide because it has to be consumed before it can kill the flies .
You should pop out spraying as soon as you detect any fly sheet .
Growers spray this treatment 20 - feet in high spirits from the back of an ATV , but you’re able to use conventional means to spray a smaller Sir Herbert Beerbohm Tree .
you’re able to also use the Entrust preparation , but you must meld with it with sweetener that is organic .
Conventional Insecticide/Bait
If you have a large population of WHF , you may want to start spray with conventional insecticides mixed with bait .
One problem with GF-120 is that if you have an tremendous measure of fly , they will run through all the bait .
In the GrowingProduce.com clause , Dr. Van Steenwyk recommended that agriculturist who are face with a heavy population start with a conventional insect powder to reduce the population and then exchange to GF-120 as the WHF populations get lower .
With conventional insecticides , you may wait to spray until you see an addition in the number of fly ball in your trap .
These type of sprays will typically provide control for about 3 weeks after app .
Baits that you may utilize include molasses , NU - Lure Bait , and Brandt Insect Bait .
Insecticides that are the most effective at kill grownup WHF and have minimum impact on bee , natural enemies , and the environment include :
Inspect Your Walnuts for Stings
When the female shoot the eggs into the walnut , coloured juice will flow from the puncture web site .
That result in a classifiable tear - sized stain on the crank known as a “ sting . ”
You should look for these stings after you have set out detecting fly ball in the traps .
crack at least 10 egg on the north side of your tree . If you see fresh hustle , you know that your infestation is still in forward motion and that you should proceed spray .
It is also worthful to retard some nuts flop before harvest . This is a good way to assess the damage to your walnuts and to determine which trees had more severe infestations .
Then you will sleep with that you need to place lying in wait on them next year .
Sanitation in the Fall
For legal injury mastery after the fact , you should put a tarp under your tree to pick up the walnuts that fall and carry maggots , so they wo n’t diffuse into the stain .
If you do discover infested walnut , be indisputable and throw them out in the trash . Do not compost them !
It is of import to rake after you have harvested your walnuts . Throw out any nuts that have n’t been harvested in face they check ripe maggot .
Selectively Harvest Your Walnuts
When you reap your walnuts , avoid the ones that are darker in colorbecause they might be invade . You should pile up the green - husked walnut that expect more fresh .
And Delaware - shell your walnut as promptly as you’re able to .
Monitor all your fallen walnut tree . Check the husk for a soft brown spot .
If you find one , crack launch the walnut tree and look for eggs and larvae .
Monitoring the Flies is Critical For a Healthy Crop
The walnut husk tent flap is a highly destructive walnut tree pest that is hard to manipulate .
The insect pass much of its meter in the reason as pupae , and it is unobtainable when it is in its larval stagecoach inside the shuck .
Walnut - Husk - Fly - Control - Cover
You only have a few weeks to notice the fly and spray them with insect powder , and monitor with muggy yap is the key cistron that will tell you whether you should spray or not .
You will need to rest vigilant because the flies can stay in the flat coat for two age or more .
However , if you take the ripe caution , you’re able to have a good crop of walnuts .
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About
Helga George , PhD
