Protecting Fruit Trees from Insects and Diseases Post-Webinar Q&A

Extension specialists George Hamilton and Glen Koehler answer real questions from gardeners about fruit tree pest management
apple maggot

In a recent webinar from UNH Extension and UMaine Cooperative Extension, George Hamilton and Glen Koehler delved into fruit tree pest management in backyard orchards and answered viewer questions.

We didn’t get to all of the questions viewers had for us, so we are sharing relevant questions and answers here as a written Q&A. Enjoy!

When do I spray my fruit trees?

We recommend following a home fruit spray schedule, which is going to be specific for each type of fruit you’re growing. Extension services like UNH and UMaine publish schedules specific to our region. If you’ve had particular difficulty with a certain disease or pest, you can experiment with skipping some parts of the schedule and focusing on preventing the issue or issues you’ve had, but always spray in accordance with a schedule so you’re only spraying when it can make a difference.

What are a couple products you recommend a backyard grower have on their shelf that will help manage most issues in NH and Maine? Usually by the time I notice an issue, research the right product, and find someone who sells it (usually online) and get it, I’m already too late.

Generally, identifying a new issue is something that you’ll look to prevent the next year. If you dealt with it this year, you’ll deal with it next year too. So good record keeping and planning will help.

As far as a couple products that will be really helpful, we would recommend either having one fungicide and one insecticide, or one fungicide and a multipurpose spray. Even if you use a multi-purpose spray, you will still want to stick to fungicide only until after the fruit trees have finished blooming.

When selecting a multi-purpose spray, read the label carefully to ensure it can be sprayed on all the fruit trees you grow, and that it isn’t limited to just a couple sprays per year. Check the ingredients and make sure they are at least somewhat effective for most of the issues you have. And check the pre-harvest interval to see when you have to stop spraying in preparation for harvest. A common insecticide in multipurpose sprays is malathion, which is a good choice for most issues although does not have a particularly long residual effect. Multi-purpose products will often contain the fungicide captan, which is a good general use product.

For a supplemental fungicide, you want something that targets the diseases that you want to spray for pre-bloom. Myclobutanil is a good choice as a supplemental.

What is the recommended distance between cedars and apples? Are all cedar varieties hosts? If you don't see the orange growths on the cedar can you assume that those cedars are not hosts?

Beyond 100 yards is a relatively safe distance, but cedar apple rust spores can travel up to several miles to your apple trees. Keep in mind the orange galls are only visible for part of the year. Red cedar trees and some junipers are the alternate hosts for this disease.

I can’t cut down the cedars. What else can I do to manage apple cedar rust?

Although fungicides are available to manage cedar apple rust infections on your apples, they aren't always necessary. If you do choose to spray, apply product (labeled for rust on apples) in wet springs while young leaves are expanding, and repeat at labeled intervals and rates until the trees are in full bloom. Follow label directions explicitly whenever using any pesticide. An even better way to prevent cedar apple rust is to plant resistant apple varieties such as Redfree, Liberty, McIntosh, Red Delicious, Baldwin,  Freedom, Paulared, Regent, Spartan, and Viking, or crabapple varieties such as Adams, Candied Apple, Chestnut, Dolgo, Kelsey, Sargent, Snowdrift, and Thunderchild.

Will a copper fungicide work against brown rot?

Copper would not be the best choice for managing brown rot, but copper soap (copper octanoate) or copper sulfate will have some effectiveness. Better choices would be captan, chlorothalonil or myclobutanil. The critical times to manage brown rot are the first 3 weeks after petal fall and the last 3 weeks before harvest.

Other non-chemical management strategies include removal of mummies and twig cankers during pruning.  Additionally, thinning fruitlets prior to pit hardening (60 days from bloom) can reduce inoculum for later season infection due to rapid decay of infected material. 

How often do you have to apply a complete fruit tree spray? Weekly? Monthly?

To broadly generalize, it varies depending on the time of year. Starting at tight cluster (flower buds still in tight cluster but just starting to open), you want to spray weekly but then stop before flowers open. A week after petal fall, you can look to spray every couple weeks, or potentially every 3-4 weeks if conditions are abnormally dry. The product will have a pre-harvest interval, which will dictate when you stop your sprays.

Is diatomaceous earth an adequate substitute for Kaolin clay?

No, it isn’t. Diatomaceous earth is not registered for use in this way, and we don’t believe it will be effective.

If a young peach tree (probably 7 or 8 years old) has peach leaf curl and drops its leaves, is that the same reason the fruit doesn’t develop or falls while green? Or are those two separate issues? It made beautiful peaches 3 years ago, with leaf curl and drop, but since then no fruit, very little flowering, and the flowers no longer smell like peaches when in bloom. What to do?

Peach leaf curl can be prevented, but can’t be managed once symptoms are visible. Fungicides sprayed before bud break give good control. A fungicide spray after leaves drop in the late fall will help, or you ca choose to spray when blossom buds are showing pink in the spring, before bud swell. Chlorothalonil or a copper fungicide will be a good choice.

Is it fair to assume that anything you recommend is safe for people who have beehives, who will be subject to exposure ever after the blooms are gone?

We recommend planting your fruit trees in a dedicated area, away from other gardens and away from your beehives. We also recommend keeping weeds down around your trees, including flowering weeds, with regular mowing. With proper distance and proper timing, ensuring insecticides are never sprayed before or during bloom, there should be no issue for beekeepers. One other thing to keep in mind is avoiding spraying trees on windy days, when drift is more likely.

Once fruit trees are done blooming, and if flowering weeds are regularly mowed around your trees, there will be little reason for bees to visit your fruit trees and risk exposure.

Do you have pictures of the different diseases that affect fruit trees?

PlantVillage from Penn State is a great resource for looking at photos. They have pages for all fruit and vegetable crops, with good pictures of common insect and disease issues. We give this recommendation with the caveat that we don’t recommend relying on their recommendations, but it’s useful for looking at photos and diagnosing problems.

I use surround for plum curculio.  But I want a one-time broad-spectrum spray.  I've heard the best time is when nighttime temps are at 70 F.

Unfortunately, a one-time spray with even the most effective broad-spectrum spray will not likely give full control of plum curculio. But if you were going to choose one time to spray, a week after petal fall is probably the most impactful time. A warm and humid evening when temperatures are near or over 70 degrees would be ideal timing.

What are the organic options for controlling plum curculio?

Repeated use of kaolin clay.

Do you have recommendations for controlling Asiatic beetles on my peach trees?

We don’t recommend specifically targeting Asiatic garden beetles, but following a spray program with an insecticide or multi-purpose spray will give you meaningful control.

What can you use on Japanese beetles?

Carbaryl or a pyrethroid insecticide (various names ending in -- “thrin”) ingredients are effective against Japanese beetles.  Malathion might help a little.  Even a spinosad ingredient might help some.  Spray on warm sunny afternoon to increase chance of JB contacting fresh spray. But don’t expect protection to last very long.  We recommend focusing on hand-picking and following a spray program for other insect pests, and accepting some damage from Japanese beetles.

What about planting a "dummy" crop to draw the Japanese beetles away from other trees/vines?

How are you going to ensure the Japanese beetles from visiting the trap crop but not the plants you want to protect?  It would be easier to install traps about 100 feet away from the plants you want to protect.  This will siphon off some Japanese beetles, but also attract more to your property, so it’s not always worth it. You will also have a grub problem wherever you set up the dummy crop and/or traps.

What about bird protection for stone fruit? I always see bird damage first and then Japanese beetles in the wounds.

Bird netting is about your only option. Picking as soon as fruit is ripe will also help. Get more tips here.

Should I use a dormant oil spray?

Dormant oil is useful for some specific insect pests. It is not a fungicide. Dormant oil will primarily control aphids, scale and mites.

Is bacillus subtilis a good organic fungicide?

This product may have some marginal efficacy for diseases such as apple scab, flyspeck/sooty blotch, and fire blight.

Is kaolin clay (surround) effective against curculio and maggot flies?

It can be effective for both if consistent heavy coverage is maintained.

Do you have a month-by-month schedule for fruit tree maintenance? Pruning, spraying and fertilizer and so on. I need a detailed list.

Pruning and fertilizer are very easy to add onto our spray schedule. Pruning should be done in March or early April, and fertilizer should be applied between the end of April and end of May.

This is the link to the UNH Extension Home Fruit Spray Schedule, and this is the link to the calendar for apple orchard management (which includes other activities, but is just for apples).

What is this? My 2 young pear trees’ leaves have small puckery, pimply dots. Heading into season 3. How do I ID this, and what should I be doing?

This sounds like it could be pear leaf blister mite, which usually distorts some leaves but is not particularly harmful to the tree. You can send photos to your Extension service for positive identification. See here for more information.

Is it necessary to burn pruned branches from apple trees? Is it okay to chip the branches and use them for mulch?

Best to burn if fire blight is an issue.  If not, chipping so that the wood dries might not be harmful, but we’d rather see some other mulch used just in case.

Can you please also share your thoughts on how to prevent tent caterpillars on apple trees?

When infestations are still small and accessible, tent caterpillars can be hand-picked from trees and dropped into a bucket of soapy water. As populations grow, localized nests may be pruned from the tree to prevent further damage. Open the netting covering so some birds eat the caterpillars. Remove egg masses from twigs or other sites.

Treatment for white peach scale?

A dormant oil would be a good option. Look for a dormant oil that lists white peach scale as a targeted insect pest.

We have a green lichen type on the trees.  Is that a problem?  What should we do?

Lichen is not a problem in and of itself, but indicates tree canopy may need to be opened up and thinned out with pruning.

Are a lot of woodpecker holes/activity on a tree an indicator of an issue?  It is a 10 year old Kavanaugh planted in an old compost so grew fast, now maybe 12” diameter trunk.

This sounds like damage from the yellow-bellied sapsucker, a species of woodpecker.  A tree with 12” diameter and no other problems should not bothered much by sapsucker holes.

I have 2 year old apple trees. Last summer I had some red humped caterpillars on them. I picked them off and dumped them in soapy water. Are they likely to come back? Are there signs to look for?

They are likely to come back. We recommend removing and destroying larvae from affected branches when you see them, and using localized intervention on trees severely affected. The most targeted spray you can use is with an organic biological insecticide called Bacillus thuringiensis, which is most effective when sprayed on very young caterpillars. This microbial formula affects caterpillars only (gives them a deathly stomachache) and won’t harm bees. Just remember that caterpillars are the larvae of butterflies and moths, so only spray near red humped caterpillar larvae.

Interestingly, if you see a white formation on a caterpillar, it’s been parasitized and killed by a beneficial wasp. These tiny wasps don’t sting people and are voracious predators of many pests in the garden.

For black knot, do I cut off the branch? I think it was on a plum but also on ancient apples and alder.

The black knot wouldn’t be affecting your apple, but pruning it out is the best approach. Proper sanitation of your pruning tools is critical when pruning out black knot. Learn more here.

I have 10 year old pear trees in a community garden that had what i think is fire blight last year.  At first we thought the trees were just dry then we tried to cut out all the branches with leaves that looked burned but pretty expansive and not sure if we got it all.  What should we look for this spring?  Any chance we can save those trees?

This year check often starting about a week after petal fall and remove any dying branch tips or shoots as soon as you see them. In a community garden, your options are very limited, but keep the trees well watered and consider removing them if there is severe fire blight infestation.

When I cull apples to remove ones with insect damage, I throw them into a field about quarter mile away for the deer to eat. Is that far enough for curculio?

No, that’s not far enough. Plum curculio can easily fly that far.  Soak the fruit in water until they rot, bury or compost them.

I need to combat Oriental Fruit Moths on my peach trees. I’m interesting in attacking with sprays, but I was wondering if you have other advice. I’ve heard these are hard to beat with many of the general purpose sprays. Do you know whether parasitic wasps can be effective as well? Will sprays be able to protect tree tips too?

Purchasing parasitic wasps is not an effective strategy for home gardeners. The wasps will not stay in your yard.

The non-chemical option is a substance called kaolin clay, found in a product called Surround. Surround WP Kaolin Clay forms a barrier film on the fruit, which physically prevents the moths from gaining access. It can be a bit challenging to apply, but is applied using a sprayer just like a chemical control would be.

For a chemical option, we recommend a product with the active ingredient malathion.

Timing is very important. You want to do your first spray when the petals fall from your tree. That’s typically in the second half of May. Then you spray every two weeks into the middle or potentially end of June. So, you’re looking at spraying 3 times, give or take, with either kaolin clay or malathion.

The timing should be roughly the same for your cherry trees.

You can also use a multi-purpose spray that contains malathion and a fungicide.

What’s important is that you wait until the trees are done blooming before spraying. You should also pick a very calm day for your sprays, and of course follow all label instructions. If you go for malathion, you need a product registered for use on both cherry and peach, and that is registered for oriental fruit moth.

Is there an organic product or home mixture  to keep gray squirrels from stealing peaches and apples?

Organic or not, there aren’t any products that are known to work. About all you can try is using capsaicin hot pepper spray, but there will be residue on your fruits.

It is nearly impossible to keep squirrels out of fruit trees because of their superb climbing and jumping ability. Sometimes if there are other unprotected fruits available, you can protect the crop of a single tree by netting it as you would to exclude foraging birds. While squirrels can readily gnaw through the plastic netting, they may not persist if enough alternative food is easily available. Source: UCANR

Do you suggest using Neem oil?

Neem oil is not effective against the major insect pests like plum curculio or apple maggot.  Neem butter paste might help reduce round headed apple tree borer attacks. Neem may help control certain soft-bodied insects and may help with certain fungal diseases like brown rot.

Got questions? The Ask UNH Extension Infoline offers practical help finding answers for your home, yard, and garden questions. Call toll free at 1-877-398-4769, Monday to Friday, 9 a.m. to 2 p.m., or e-mail us at answers@unh.edu.