Wednesday, April 27, 2011

Peach Leaf Curl

From the garden e-mail bag, Kristi is not a big fan of curling (the disease, not the sport): "In the last two years I’ve planted several fruit trees. But right now, I am very concerned about my peach tree. It appears to have leaf curl. Everything I am reading on peach leaf curl tells me that I need to treat in the fall or the dormant season. I am wondering if it is OK to treat the tree with a fungicide now. Or, is it best to just leave it alone this year and treat it in the fall? Also, what is the best thing to use?"
Although it's still early, it looks like we have a 2011 winner in the informal, "What's Bugging the Backyard Gardener" sweepstakes: peach leaf curl. Just about everyone knows of a nearby peach or nectarine tree that is suffering greatly.

Peach leaf curl causes leaves of peaches and nectarines to discolor, thicken, pucker, curl, distort and eventually fall off. The fungus overwinters in these trees as spores, usually in the new buds. The rains of late winter and early spring - or in the case of 2011, the abnormally wet weather of March - splashed these spores onto the emerging leaves, causing more problems. Emerging shoots can die; fruit production can be reduced in severe infestations. Only rarely do reddish, wrinkled areas develop on fruit surfaces; later in the season these infected areas become corky and tend to crack.
         The good news is that a second set of leaves soon emerges and can develop normally when the rains cease and daytime temperatures steadily reach into the 80's. 


 Studies at UC Davis have shown that nipping off infected leaves of peach and nectarine trees doesn't do much good this time of year.

If your peach and nectarine trees are showing signs of peach leaf curl now, the best thing you can do is to assist those trees through this stressful period. 

• Rake up any fallen leaves and pull weeds that are growing beneath the drip line of the trees.

• Fertilize the area thoroughly, if you haven't yet done so. 

• Before the weather heats up into the 90's, spread four inches of fresh organic mulch beneath those fruit trees. Organic mulches, such as compost, shredded branches or the fallen leaves of healthy shrubs and trees will help conserve soil moisture, hold down weeds and add nutrients to the soil as that mulch breaks down.

• According to Steve Zien of the Sacramento-based organic garden consultancy firm, Living Resources, there now appears to be a method for control after the leaves have developed peach leaf curl.  Evidence indicates strong foliar applications of quality seaweed fertilizers (containing Ascophyllum nodosum) on distressed foliage can, in some cases stop the spread of peach leaf curl.

"Our findings indicate that foliar applications of seaweed (Maxicrop brand seaweed) can result in approximately 80% control of peach leaf curl," says Zien.  "A mixture of one part Maxicrop liquid concentrate to ten parts water was applied two to three times during early spring.  Following treatment new leaves developed normally.  Meanwhile, unsprayed trees and trees sprayed with water, continued to develop disease symptoms. Leaves damaged prior to treatment will remain distorted.  However, the leaf thickens, becomes greener and remains on the tree for a longer period of time (compared to untreated trees).  This provides the tree with vital nutrition until new healthy leaves develop.  One theory is that the seaweed thickens the cuticle (leaf skin) creating an environment not suitable for the fungus to develop." 

(2012 Note: Test results at the Fair Oaks Horticulture to control peach leaf curl during the winter of 2011-2012  showed the ineffectiveness of Maxicrop. "Compared to untreated branches, Liquicop-treated branches averaged about 70% control," says Chuck Ingels, Sacramento County Farm Advisor. "Copper soap was slightly better at 80% control, Agribon (row cover material)  by itself was less effective at just under 60% control, and both Agribon + Liquicop and lime sulfur (late fall) followed by Microcop (late winter) resulted in nearly complete control. Maxicrop (sea kelp) did not work at all and seemed to increase the severity on some of the branches.")
         The experts at UC Davis advise pruning infected peach trees in the fall before spraying with a copper ammonium complex product with 1% horticultural spray oil added to the mix.

     And now here's the bad news about sprays: the copper sprays available currently are weaker (about 8% concentration). Lime sulfur has been removed from the market. Bordeaux mixtures are expensive and wasteful...and potentially caustic.

In the good old days of fruit tree sprays (2009), 50% copper concentrates were the recommended course of action. Not any more.
The UC Davis Integrated Pest Management information on controlling peach leaf curl says, "Fixed copper products include tribasic or basic copper sulfate, cupric hydroxide, and copper oxychloride sulfate (C-O-C-S), but currently only liquid products containing copper ammonium complex products with 8% MCE (e.g., Kop R Spray Concentrate [Lilly Miller brands] and Liqui-Cop [Monterey Lawn and Garden]) are available to consumers. The most effective copper product, 90% tribasic copper sulfate with a 50% MCE (Microcop) is no longer available to retail outlets, because the manufacturer withdrew the product in 2010, although remaining supplies still can be sold."  

One of the reasons for that removal: repeated annual use of copper products over many seasons can result in a buildup of copper in the soil, which eventually can become toxic to soil organisms, and if it moves into waterways, can harm some aquatic species.

The removal of lime sulfur products was prompted by a rash of self-inflicted deaths in Japan in 2008 called "Detergent Suicides", which has since spread to the United States.

Bordeaux mixtures, a combination of copper sulfate, hydrated lime and water, are effective in controlling peach leaf curl, but come with their own set of warnings. According to the UC IPM Guideline entitled "Bordeaux Mixture":  "When applying Bordeaux, be sure to wear protective clothing, including goggles, because the spray deposit is corrosive, can permanently stain clothing, and is difficult to wash off." They also recommend wearing a dust and mist-filtering respirator when mixing in the hydrated lime. And that mixture can discolor anything it touches, including buildings and fences.

Although you can purchase pre-packaged Bordeaux Mixtures, they are not as effective as the mixture made from the individual components, reports that UC IPM Guideline. And that brings up the cost and waste involved: copper sulfate and hydrated lime are usually sold in large quantities, much more than the average homeowner needs for the backyard peach and nectarine trees. Storage involves mixing the leftover individual ingredients separately in water and storing in their own sealed jars. That UC IPM Bordeaux Mixture Guideline warns: "Be sure to clearly label both stock solutions and store them where children can’t get into them, since these materials, especially the copper sulfate, are very toxic and corrosive."

The synthetic fungicide chlorothalonil is the only non-copper fungicide available for managing peach leaf curl in the backyard orchard. Although one fall application may help prevent a spring outbreak of peach leaf curl, a second application in January or February, as the buds begin to swell, can be beneficial, as well.

But be sure to read and follow all label directions if you choose to use chlorothalonil, including this
"This product is toxic to aquatic invertebrates and wildlife. Do not apply directly to water or to areas where surface water is present or to intertidal areas below the mean high water mark. Drift and runoff from treated areas may be hazardous to aquatic organisms in neighboring areas."

Or this:  "May be fatal if inhaled. Harmful if swallowed or absorbed through skin. Causes moderate eye irritation. Avoid contact with eyes, skin or clothing. Do not breathe spray mist.

Or this: "This product contains chlorothalonil which is a
chemical known to the State of California to cause cancer."

No matter which spray method you choose, several days of dry weather must follow for the products to work. And that is one of the reasons the peach leaf curl breakout this year in Central and Northern California is so vexing: even though gardeners may have applied a spray, there were very few windows of opportunity (clear weather). If it wasn't raining this winter here, it was foggy. 
         There are peach varieties that are more resistant to peach leaf curl. The downside: they may not be as flavorful as you might like. Peach varieties reported to be more leaf curl resistant include Frost, Indian Free, Q-1-8 and Muir; among nectarines, only the Kreibich variety is resistant, says UC Davis.


Saturday, April 30, 11 a.m.-1 p.m. See you at Davis Ace Hardware, 240 G. St. in Davis. Yes, there will be peach leaf curl questions. I'll be the one standing by the bags of Black Gold potting soil. Staring at a peach leaf sample.

Sunday, May 1, 1-3 p.m. See You at Emigh Hardware, 3555 El Camino (just east of Watt). Come on out and let's talk gardening! Brought to you by Grower's Gold growing mixes.


  1. What, if anything, happens to the fruit?

  2. Is there such a thing as apinach leaf curl? My neighbor brought over a bunch of spinach from her garden, each leaf was the size of a catalpa leaf (very big) and it looked bubbly..the leaves were really deformed....I thought maybe it was all the rain we've had, does anyone know what could cause this?

  3. There are curled leaf spinaches.
    Can this problem or something similar effect wisteria? I'm trying to determine what is wrong with one of my two vines.

  4. Fred, I'm glad you wrote this because it's going to be a blog topic sooner or later. My two peach trees just got NAILED bad with leaf curl this year -- even though I sprayed Liqui-Cop twice during the winter months. The final application was in late February -- just as the buds started to expand and then we got hit with two weeks of rain. End result? Leaf curl -- bad. Never seen it this bad before. Oddly enough? The three nectarine trees out front were barely affected. Perhaps it's because they were close to the house? Perhaps because they DID have a layer of mulch (bark) where the two trees in back did not? Thanks again for posting this. Glad I'm not the only one...

  5. Fred - thanks for this. It makes me feel better about how bad my tree looks this year. After reading all the warnings on those products, I think I will just learn to live with the problem as the cure seems just as bad.

    I am very tempted to remove my peach tree though and plant a different kind of fruit tree that will do well in our area without needing so much pampering to perform well.

    1. Hi Chad,

      Try spraying with oregano oil before you pull the trees out.

  6. So happy to hear I'm not the only one!!!!!!

  7. I have a tree with a multi-graft, Frost, Q-1-8 and Indian Free. Never see the curl on them, and they are delicious. I still nurse along the donut peach, it gets it badly, because I just love their cute little shapes. And yes, Seaweed does help.

  8. Auntmary/Maybelline - aphids can cause distorted, curled new growth on plants. Look closely at the emerging leaves to see if there are aphids nestled in there.

  9. Good Rant Fred thanks. I have the same issue as Bill Bird with my nectarine trees. With all the heavy rain at bud swell they get leaf curl no matter how much liquid-cop I use over the winter. (We need to get the good copper back into production.) Is there a point leaf curl gets so imbedded into the tree that it should be pulled and start new?

  10. fred - my trees have been in the ground for 3 years now, and i thought i was doing something right as the curl never showed, until last year - a wet one, and only a little bit. this year, we have a raging case of the curl. so it looks like i will have to do fall spraying going forward. another change in the garden. i have started growing clover in the orchard as a cover crop to draw in beneficals - this certainly increased the dew level and thus provided a spring board for worsening curl. i wonder if i went back to bare ground, if i would see a natural decrease. who knows. no i am off to find the remaining 50% copper solutions....

  11. Are these chemicals the only way to having fruit trees that product fruits and have a healthy plant? I garden organically and my dwarf peach tree produces little fruits that fall of before they mature. I have experienced curling on a few leaves and pulled them. It just doesn't make sense to grow instead of buying fruit at the store if I have to treat them with chemicals and risk those chemicals on my other organic plants.

  12. We too are having trouble with peach leaf curl on our young tree. An acquaintance suggested spreading rabbit droppings around the base of the tree. A neighbor who has rabbits happily obliged. I picked off the bad leaves and spread it around a few weeks ago. To soon to know if it helps but wondering if anyone out there has heard of such a thing. He seemed to think it is common knowledge.

  13. Although I sprayed them as suggested too, we got the leaf curl several years ago in both a peach and plum tree. These trees gave buckets of excellent fruit every year till then, and even the first few years the fruit and fruit production went down but was still okay. Last year we got nothing and I gave up can removed them. Maybe you will have more luck!

  14. Fred great article, I live in the state of WA and my 4 peach trees had leaf curl so bad last year I thought I would lose them. Very rainy and cool. I think our first 70 degree day was in late June. An orchardist friend of mine gave me some "Bravo" and I sprayed last summer and it knocked the leaf curl down. I sprayed again in late October when just about all the leaves were gone and then again the last week in February. My trees are just starting to leaf out and it looks like they are mostly free of leaf curl.

  15. I live in Spain and I planted 3 new nectarines at the start of a very dry winter followed by the usual very dry summer. Watered at the roots - and - they have ALL got peach leaf curl. Or at least I guess that's what it is. There are tons of ants among the damaged leaves. I guess I will try the seaweed spray, unless anyone has a better idea ?

  16. Anyone aware of whether spraying fresh lime juice on dormant branches is effective?

  17. Ants among the leaves (comment July 22 12) could mean large colonies of aphids. Aphids get out of control very quickly and are most effectively controlled BEFORE they curl the leaves. The big black aphids i see on my orchard usually appear on leaves near the base of a plant, 1 - 3 weeks after leaves emerge in spring, and ants support and farm the colonies!

  18. What about ZIRAM? I know it is used on orchards with good results

  19. I read somewhere that a 1:10 solution of household bleach will not harm the plant and will kill the PLC.
    My tree has been suffering for 4 years, and I get poor fruit. I'm going to try it.

  20. Back to the Wisteria curling prob mentioned earlier.....any advice??

  21. Has anyone tried a diluted bleach solution? I had a terrible case of fireblight on some apple trees and sprayed with diluted bleach/water and it completely took care of it....I'm wondering if the same would be true of curly peach tree leaves?

  22. Hello,
    Every one not knows about pruning a trees & according to expert advice pruning infected peach trees in the fall before spraying with a copper ammonium .ccording to organic garden consultancy firm, Living Resources, there now appears to be a method for control after the leaves have developed peach leaf curl. in some cases stop the spread of peach leaf curl

    "davis tree removal"
    davis tree care"

  23. Well! It makes me feel better about how bad my tree looks this year.

  24. To keep the ants out of your fruit trees wrap the bottom/trunk of tree with rosemary cuttings.I notice that the ants will leave,i guess they hate the smell of rosemary. .All my fruit trees are ant free now,also add new cuttings every year.

  25. are these copper fungacides poisonous to the fruit and ultimately to humans?

  26. Is there such a thing as cherry tree leaf curl?
    Every year the affected areas have black bugs that I assumed were aphids, along with carpenter ants. I thought they had a symbiotic relationship, and am trying to eliminate the carpenter ants, thinking that they were fending off natural predators.

  27. I was using Bonide copper fungicide which states it is for organic gardening. However, the copper compound doesn't seem very healthy to people, animals, or the environment to me.

    After some searching, I came across trichoderma harzianum to be used as a foliar spray, but it is pretty pricey on it's own and in products that contain it.

    Finally, I stumbled across Actinovate & Bayer Serenade which are biological fungicides that say they can be used in organic gardening. However, they too aren't exactly safe for people or the environment either.

    I read about the 1:10 solution of household bleach but haven't tried it.

    I've also read oil of oregano is supposed to be effective which I will try this year during the dormant season. Will boil dried leaves to make a tea to save money over the essential oil.

  28. I have used Oregano oil - I went to the grocery store and bought oregano. I made it into a tea with hot water and filtered off the 'leaves' through a sieve. I sprayed the infected tree and this seemed to stop the disease. I then came across a PATENT claiming that Oregano oil at the rate of 8 ml per gallon of water does the trick. You can buy the oil in some Health Shops.

  29. Copper Fungicide by Captain Jack's is available at Home Depot containing 10% Copper Octanoate (Copper Soap). Is it safe and effective? This ingredient is not listed with the other copper products in the article.