Plum Curculio


Looks optimized for apples.


I just scanned posts saying there are not many effective pesticides for curculios that can be used in urban area. There’s one that very effective, and it’s safe for bees if you do it right. The product is malathion. Spray the malathion on the trees and on the ground around the trees at dusk. Malathion is a contact insecticide with a relatively low human toxicity rating. It is almost instantly deactivated by the combination of oxygen and sunlight hence the need to apply it at dusk after bees have become inactive Two of my plum trees are too big for me to reach the tops. In fact the Mariana tree is 30 foot tall and I can only reach the bottom limbs even with a latter. No problem, the curculios are still either low in the tree or on the ground at this time of day. The malathion will get them on their way up the tree through the night.

Do this at least once every two weeks from the time the little plums are half the size of blackeyed peas until they are about the size of a quarter than you can stop. Check the little plums first thing every single morning for the crescent moon scars of a curculio egg being laid. If you see a scar spray the tree right then. The curculio might still be in the tree, but if malathion is applied within a few ours of the egg being laid it will prevent the egg from hatching. Come back at dusk that evening and spray the tree again to make sure you get that curculio. Then return to the two week schedule or until you see damage again and repeat. This works just fine.

Malathion will be inactive by the time the bees come out. It does not stay in the environment long at all. In many states you can use it and still call the fruit “organically grown” because it so completely goes away. It stinks, so bees stay away from it anyway. It’s relatively safe to you. It will stink up your yard for a couple of days. But for me, that’s OK. Lastly you get to stop using it weeks before the plums are ripe. Importantly it’s cheep. For the home gardener Malathion is the way to go to control curculios in my opinion.

Marcus Toole


I don’t have the gumption to try malathion again as it was such a disaster for me, my peaches and for pc control. I did not spray it as you described. It would be interesting to see if others had the same success following your steps.


It does not work at all if you spray it at the wrong time of day because the curculios are not on the tree, and it only remains active for about ten minutes in bright sunlight. It must be applied at dusk so it can stay active through the night while the curculios are doing their thing or first thing in the morning in the case of an early morning discovery of damage. You are just wasting money and putting bees at risk spraying it in bright daylight.


It took me several disastrous seasons as a young man to figure this out. It was when my dad explained that you spray peas in the late afternoon to protect bees and then learning a few years later that curculios are only out at night and malathion goes away so quickly in sunlight that I put the three bits of information together. It’s extremely effective if you spray it at the right time of day. This might pose a real problem for a large commercial operation on account of the window of opportunity being small. Maybe a commercial grower has the option of going all night if their equipment can spray into the tops of the trees. But for the home grower with just a hand full of trees, this is the best way to control curculios in my opinion. Spray at dusk, spray as many branches as you can reach with a latter and spray the ground and trunk. Usually you will pretty much get all of them, at least for that week.


@coolmantoole I am intrigued, what brand of malathion do you use? I have never used it.


I’ve used several and they all seem to work the same. I would not buy one that comes in a white or clear bottle since it breaks down in sunlight. The brands I have used have all come in black or dark brown bottles that protect the product from light.


Thanks for posting. Adding the details as you did will help others.


Relatively is the operative word here. It’s oral LD50 in rats ranges somewhere from 1000-10000 LD50 according to Extoxnet. That’s pretty non-toxic for an organophosphate but that doesn’t tell the whole story. It’s toxic enough it would never fall into the EPA reduced risk certification. Malathion 57 has a “WARNING” signal word on the label, which is fairly toxic to mammals by EPA standards. WARNING is just one step down from a DANGER/POISON signal word. When an applicator sees WARNING, they know to take a little extra care with the pesticide concentrate. 50% Malathion formulations carry a less severe “CAUTION” on the label.

Further complicating things is that it takes considerably more active ingredient of Malathion to kill pests. This is significant because many other insecticides may have a more toxic profile in terms of LD50 values of the active ingredient, but take much less active ingredient to kill the pest, which significantly limits the applicator in receiving a harmful dose. As an example, Mustang Maxx I occasionally use (also carries a “WARNING” signal word on the concentrate) requires only 4 ounces/acre. I spray at 100 gal./acre so that’s 4 ounces of chemical/100 gallons of water.

Malathion 57 is labeled at 32 ounces per acre, 8 times the amount of chemical concentrate vs. Mustang.

However, that doesn’t tell the whole story because Mustang has about 9% active ingredient in the concentrate, while the Malathion I referenced has 6 times the active ingredient in the concentrate (57%). That means while applying I am using about 50 times more active ingredient of malathion vs. Mustang.

I’m not saying I would be afraid to use Malathion (I have used it) but it’s not as safe as it might seem when you examine the whole picture.

I’m not trying to be contentious but I’d be interested to see any state organic certifications which allow the use of Malathion. Most of the state certifications use the USDA rules, which would prohibit the use of Malathion. I’ve heard of emergency exemptions for some compounds in organic certification programs, but I’d be surprised if Malathion was ever allowed in a federal or state certified program.

Again, I’ve nothing against Malathion if it works for you (and I think your spray program is clever in that it gets the most out the Malathion) I just don’t want people to come away with the impression that it’s as safe as it seems.

Lastly, I wouldn’t say that Malathion, “will be inactive by the time the bees come out”. Again according to Extoxnet, the half life of Malathion in sunlight is 1.5 days. That means if sprayed at night Malathion will have more than enough potency to kill bees in the morning, if sprayed on blooming weeds. That said, the extremely short half-life in sunlight does make Malathion a more bee friendly choice than a lot of insecticides.


A good thing about malathion is that it stinks. I’ve watched the bees the next morning. They stay way clear of the sprayed areas for quite some time. That’s a problem if you want a plant to get pollinated in a couple of days.


Early yesterday morning I saw one PC on my Guthrie blooms. He looked like it was just waiting for the fruit to get big enough to implant its egg. If the weather stays favorable I might have enough plums to consider your spray method.


I have used malathion and found it works well but only in acidic water. If I used straight tap it didn’t work at all. Acidic water extends the half-life. Here PC isn’t bad, a few good sprays and my fruit is clean.


Maybe that explains why it worked so poorly for me last year. I know there’s at least one thread on the board about acidifying water, but I’ve already decided to switch to zeta cypermethrin for this year.


Since it only needs to be acidic for a short time vinegar works well, add it before you add anything. Also not all, but most pesticides have long lives in acidic water.

Here is an old guide


it never ends… I like this one.


I bought a bottle of seven with cypemethrin. It appears to kill for several weeks so I would guess that it would be effective against PC.


That’s exactly what I bought. Since we are both in the same general area, and using them to treat the same fruit, perhaps we’ll have some useful data by the end of the season on its effectiveness


Ew! Thanks for the tip. Another use for apple cider vinegar!


I picked off the last few dozen late flowers and sprayed my peach trees with permethrin this evening. As i was spraying i saw one of the pc crawling off a peach that was past shuck split. He looked a little parched so i provided him with something to drink. My bloom was spread out this year so on one tree i have most fruits that are only halfway to shuck split while maybe 5-10% are past that point and probably getting hammered by pc. Hopefully i’ll be able to sort it all out when i thin and bag in a couple of weeks.


Where are you located Barry?


I’m in alabama.