Peach Leaf Curl: Symptoms and Control

In this article we will discuss about:- 1. Introduction to Peach Leaf Curl 2. Symptoms of Peach Leaf Curl 3. Causal Organism 4. Disease Cycle 5. Control.

Contents:

1. Introduction to Peach Leaf Curl
2. Symptoms of Peach Leaf Curl
3. Causal Organism of Peach Leaf Curl
4. Disease Cycle of Peach Leaf Curl
5. Control of Peach Leaf Curl

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1. Introduction to Peach Leaf Curl:

Peach leaf curl disease is distributed throughout the world wherever peach is grown. The disease received its name on account of its characteristic effect on leaf —curl. There is no definite knowledge of the place of origin of the disease. But it is believed to have been introduced in the European countries far back in 1841 from China, the original home of the peach.

The disease is now widely distributed in Europe and in the United States, in parts of Asia, China and Japan, arid also in Africa Australia, and New Zealand.

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2. Symptoms of Peach Leaf Curl:

The disease affects leaves, tender growing shoots and very rarely flower parts and fruits. It is most conspicuous on the leaves.

The disease first appears although relatively inconspicuous in symptoms, in the early spring when the leaves begin to unfold. Soon after the leaves are well out of the bud some of them appear to be distorted, puckered along the midrib and curled up (Fig. 362A) assuming a red tint. Leaf blade and petiole may both be involved in the curling.

While in more heavily infected leaves the curling is so severe that the whole lamina with the excep­tion of the tip looks like a partially inflated paper bag. The blistered portions of the leaf are softer than the disease-free parts of the leaf blade. Only a few leaves of a tree may be affected or the infections may be so numerous as to involve almost the entire foliage.

The individual lesions may include a small portion of a leaf or its entire sur­face. As the disease progresses, the leaf tissue becomes yellowish and shows some red­dish colour. The reddish-velvety surface of the lamina soon becomes whitish-grey. The leaves gradually turn brown, wither and fall off.

In heavy infections the trees may suffer severely from premature defoliation. The loss of leaves is recovered by a fresh crop of leaves produced from dormant buds. Twigs may also be affected. In­fected twigs become pale-green to yellow, swollen, stunted, sometimes exude gummy material and ultimately die. Flowers and fruits when infected drop promptly.

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3. Causal Organism of Peach Leaf Curl:

Taphrina deformans (Berk.) Tul. That the disease is caused by an ascomycete, at that time called Exoascus deformans was first described by the Rev. M. J. Barkeley. The old generic name Exoascus is still in use by many authors. The fungus does not produce any ascocarp.

An intercellular, septate myce­lium is quite common in the infected host tissue. The intercellular mycelium travels across the mesophyll and proceeds to spread out chiefly between the palisade layer and the upper epidermis (Fig. 362D), where it develops in greater abundance than in any others parts of the leaf.

In preparation for the reproductive stage, the branches of the mycelium which become established between the epidermis and mesophyll how make their way between the epidermal cells to form a network of short cells beneath the cuticle.

The cells of the hyphae are with dense cytoplasm and two nuclei. The subcutaneous and intercellular hyphal cells become uninucleate resulting from karyogamy. These are the ascogenous cells from which asci are developed. The up­ward growth of the developing asci raises the cuticle, and this is either pierced or torn and disappears, leaving the asci exposed to the surface as a more or less continuous hymenium.

In section the asci appear as a palisade-like layer (Fig. 362B). The asci are usually flattened or somewhat truncate at the free end, broader above than below usually eight unicellular ascopores are formed in each ascus, but occasionally the ascospore number may be only two.

The ascospores are forcibly expelled through an apical slit or rupture in the ascus and may accumulate on the surface of the leaf, giving a white or greyish powdery condition.

They commonly germinate by pudding to form a series of uninucleate thin-walled secondary spores which are also known as conidia. The ascospores may also germinate directly by the formation of term tubes. The young hyphae become binucleate in the host tissue.

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4. Disease Cycle of Peach Leaf Curl:

The incidence of the disease is associated with comparatively low temperatures such as occur in the spring. The optimum temperature for the growth of the fungus is about 20°C. Opinions differ with regard to the method by which the fungus survives from season to season.

For a long time it was believed that the fungus existed as a perennial mycelium in the twigs, the fungus attacking the leaves again at the opening of the buds. The general opinion is that the primary infections which occur at the opening of the buds in spring are effected by spores, probably by conidia, which have been sheltered on some part of the host or may also persist in the soil or in the soil cover.

Germ tubes from ascospores or conidia penetrate the young leaf directly into the cuticle or pass through the stoma (Fig. 362C). The fungus makes its initial growth within the cuticular layer and then sends hyphae between the epidermal cells. Ultimately the hyphae become established as intercellular myce­lium.

The first effect of the mycelium is to irritate the host cells and stimulate them to an abnormal activity. The infected host cells increase in size and change in form and structure. The affected cells suffer almost a complete loss of chlorophyll accom­panied with puckering with the midrib behaving like a puckering string.

Peach being a host of economic importance, economic losses at one time may be very heavy. But this is one of the diseases which is rather easily controlled with the adoption of proper protective measures.

Diseases cycle of Peach leaf curl is presented in figure 363.

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5. Control of Peach Leaf Curl:

A single application of Bordeaux mixture, at the right time—which is just before the buds begin to expand in the spring— can almost completely suppress the disease for the year. The disease can also be effectively controlled by a single application of lime-sulphur (5: 50) and Burgundy mixture (10 oz. copper sulphate 11 oz. soda: 3 gallons of water).

A dormant spray of Bordeaux mixture of 6: 10: 100 with lubricating oil as an adhesive in the proportion of 3 gallons of oil to each 100 gallons of mixture is also very effective. Spraying during December or before mid-January with Bordeaux mixture (6: 6: 50) before the buds burst, or with lime sulphur (1: 8) before the winter buds swell also produces good result.

The application of a very alkaline Bordeaux mixture with casein as an adhesive at the beginning of winter is also recommended as a control measure of the disease.

The spray application with Blitox-50 after harvest or before the leaf-buds swell also produces effective results. But in any case it is useless to spray chemicals when the leaves have already opening. Besides these spray applications, cutting out infected shoots and removing and burning of all infected leaves adequately control the disease incidence.