Peaches and Leaf Curl

Peaches with their leaf curl have long been a persistent concern in my orchard. I wrote about this problem a few years ago (Read that here), but since then my thinking has evolved, and I have learned a few more things along the way.

Over the years, I have observed that peach leaf curl is primarily a fungal disease. In some cases, however, I have also seen aphids and other insects causing the leaves to curl. Rarer still are insects that seem to take shelter inside leaves that were already affected by fungal leaf curl.

When some says peach leaf curl, it always refers to fungal. Taphrina deformans, the fungus responsible for peach leaf curl, is a frustrating visitor every spring. Horticulturists often recommend copper-based sprays in autumn or in late winter before the buds begin to swell. My concern has always been the possibility of excess copper building up in the soil, causing pollution and harming beneficial fungi in the process. My fears may be misplaced, but they are with me all the same.

A few years ago, I stopped spraying fungicides altogether. Instead, I chose to do the hard work myself. During the period of active leaf growth, I removed the infected leaves by hand and disposed of them away from the orchard, never in the compost pit. I enriched the soil around the peach trees with plenty of vermicompost and made sure that during dry summers the trees never went thirsty. In autumn, I collected every fallen peach leaf and again disposed of it away from the orchard. These efforts gave the trees enough strength to keep producing healthy new growth while also helping to reduce the fungal spores around them. I did try a foliar spray of Trichoderma viride, but for me it was largely a wasted effort. It seems to work better in the soil than on the leaves. A foliar spray of Bacillus subtilis appears to help a little, though only modestly. At present, I have resumed spraying copper sulphate mixed with agricultural lime, though just once every two or three winters, before spring begins. I keep the use minimal and directed only at the diseased trees. Though it is considered an organic option when compared with many commercial fungicides, but I must admit I am still not very fond of it.

Insects, especially aphids, can also cause peach leaves to curl. The difference is in the word play for novices. Fungus causes Peach leaf Curl disease. Insects may cause the leafs to curl, but it is not called leaf curl disease. I noticed the insects causing leaf curl, a few years ago, and they have returned again this year. The leaves are beginning to curl, and when I plucked one and examined its underside, I found clusters of aphids feeding there. They suck the sap and cause the leaf to curl. Their damage is somewhat different from fungal leaf curl. Leaves affected by aphids are usually only mildly curled, while fungal leaf curl tends to produce thick, fleshy, heavily distorted leaves that often turn reddish.

The first thing I do now when I notice aphids is look for ladybirds. Usually, a healthy population of ladybirds is enough to keep aphids under control. Small birds such as tits also feed on them. But when aphids are numerous and natural predators are absent, I prefer to spray neem oil mixed with a little detergent, after most of the blossoms have finished. The results take a few weeks to appear. Interestingly, neem oil also has mild antifungal properties. After that, I apply Metarhizium anisopliae to the soil around the tree. Although it is mainly effective against root grubs and other soil pests, it also seems to help reduce aphid numbers when used alongside neem oil.

Another mistake I have made is planting plums close to peaches and nectarines. Because they are closely related, the pests and diseases that affect peaches can also affect plums. In a mixed orchard where they grow near one another, control becomes a little more difficult. This is especially true in orchards where curculio is a problem, though thankfully that is not an issue in our part of the world.

To summarize, a healthy ecological balance and good orchard hygiene are often enough to reduce fungal leaf curl and keep insect-driven leaf curling under control. Some people choose leaf curl resistant cultivars. That certainly helps, though it also means giving up some of the wide range of flavours that peaches and nectarines can offer.

So, off to spray some neem oil now. After that I will go for my stroll in the orchard, checking out the other nooks and corners here.

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