A Detailed Guide to the Causes of Grape Berry Rot and Its Control Measures

Growers who have grown grapes usually encounter the phenomenon of grape berry rot, especially in the middle and late stages of grape growing. Once berry rot occurs, it seriously affects grape yield and quality, bringing great economic losses to farmers. Therefore, Qinong Network has brought you an analysis of the causes of grape berry rot and how to prevent and control the phenomenon of grape berry rot.

1. Causes of the disease

1. Pathogen infection. The main diseases causing grape berry rot are white rot and anthracnose, and in special years there is also black rot. White rot and black rot not only cause rotten berries and rotten clusters, but also infect grape canes and tendrils, forming brown lesions; in severe cases the diseased branches and leaves wither and die, and the tree vigor weakens, affecting the fruit yield and quality of the current year and the following year.

2. Adverse weather. In the Central Plains region, rainfall is concentrated in July—August, and this period is exactly the middle and late stages of grape fruit growth. The climate characteristics of high temperature, high humidity and frequent rain at this time easily cause widespread outbreaks of the above three diseases.

3. Improper orchard management. Most vineyards in the Central Plains region use trellis-arm training. Although summer management is convenient, the dense branches and leaves inside and outside the entire trellis easily lead to poor ventilation and light penetration, and most fruit clusters are exposed outside or crowded among the canes. Coupled with abundant rain and muggy air, a microclimate of high temperature and high humidity easily forms within the trellis. If mechanical wounds are further caused by storms, hail, sunburn, fruit cracking or birds and insects, the epidemic of “berry rot disease” will be aggravated and secondary diseases will be triggered.

4. Weak tree vigor. The following factors all cause weak tree vigor and poor disease resistance: insufficient application of organic fertilizer, excessive application of nitrogen fertilizer, and neglect of nutrients such as phosphorus, potassium and calcium; unreasonable summer pruning, with vine tying, pinching, shoot thinning and cluster straightening not done in time, resulting in poor nutrient supply during the fruit growth period; too many ineffective branches and leaves, causing excessive ineffective consumption; too many fruits hanging on the tree, and weeds growing in profusion under the trellis; severe pests and diseases, etc.

2. Control measures

1. Change trellis-arm training to a small shed trellis to create a microclimate unfavorable to disease occurrence. A small shed trellis with single dragon-trunk or double dragon-trunk training and medium-short shoot pruning should be adopted. It must be ensured that the light on the shed surface is sufficient, and the leaf area index should preferably not exceed 1.5~2.0; when the fruit is near maturity, the light transmittance under the trellis should be adjusted, generally requiring about 30%. During the growing season, summer pruning, vine tying, shoot thinning, pinching and cluster spreading should be done in time, so that the fruit clusters hang in the “dappled shade” of the trellis surface, avoiding sunburn or rainwater remaining on the fruit surface, and avoiding mechanical wounds to the fruit caused by storms, hail, etc.

2. Strengthen soil, fertilizer and water management to enhance tree vigor. Apply decomposed organic manure by digging trenches in alternate years and alternate rows, preferably chicken manure, together with an appropriate amount of phosphorus and potassium fertilizer. The temperature at this time is relatively high, which not only favors the decomposition of organic fertilizer, but also gives the leaves a relatively strong photosynthetic capacity, enabling effective use of nutrients. In the late stage of grape growth, spraying a 2%~3% potassium dihydrogen phosphate solution together with pesticide application can significantly enhance tree vigor and reduce the occurrence of “berry rot.” Plant growth regulators can be sprayed according to the growth condition of the plants to improve leaf function and enhance tree vigor and disease resistance.

After rain, attention should be paid to draining accumulated water in the orchard, and loosening the soil and weeding should be done in time to prevent excessive soil humidity. For clayey soil, soil improvement should also be carried out to enhance the air permeability of the root-zone soil. Attention should be paid to raising the fruiting position, and as far as possible no fruit clusters should be left at 40~50 cm above the ground, so as to reduce the chance of pathogen infection.

3. Eliminate sources of inoculum. After autumn, before the canes are taken down from the trellis, remove the diseased residues in the orchard and burn them in a centralized manner. Before burying the canes in soil for winter protection in autumn and after they are uncovered in spring, spray 50~100 times dilution of Suolibaer or 3~5 degrees Baumé lime sulfur mixture + 300 times dilution of sodium pentachlorophenate to eliminate sources of inoculum. During the growing season, promptly remove diseased leaves, diseased fruits and diseased canes, and bury them deeply in a centralized manner.

4. Strengthen trellis surface management. Pay attention to timely vine tying and pinching to maintain ventilation and light penetration within the trellis. Determine the yield according to the growth condition of the plants; generally, for a mature orchard, the yield per 667 sq m should be controlled at 2,500~3,500 kg.

5. Chemical control. For infected vineyards, before the tree buds, spray the tree body or the ground with 2 degrees Baumé lime sulfur mixture + 200 times dilution of sodium pentachlorophenate, or 500 times dilution of 50% thiram wettable powder, to provide protection and prevention.

For severely diseased orchards, in the early stage of disease occurrence, mix 1 part thiram, 1 part sulfur powder and 2 parts lime evenly and spread it on the ground under the grape trellis, using 1~2 kg per 667 sq m. For disease occurring during the growing season, spray 800 times dilution of 50% thiram wettable powder or 600~800 times dilution of 75% chlorothalonil wettable powder, spraying once every 10~15 days throughout the growing season, but be careful to alternate and rotate the pesticides.

For orchards with severe disease in the previous year, before disease occurrence, spray under the trellis with 500~600 times dilution of thiram or 500~600 times dilution of 50% carbendazim to eliminate the inoculum overwintering in the soil; during the growing season, spray Bordeaux mixture at an appropriate concentration once every 10~15 days to reduce the chance of disease infection. Once diseases such as white rot and anthracnose occur, apply pesticides according to the symptoms, but be careful to alternate the pesticides. After the fruit colors, to prevent pesticide contamination of the fruit clusters, 600~800 times dilution of 12% copper green emulsion can be used for spray control of the diseases.

The above is the collection and arrangement by Qinong Network of the causes of apple berry rot and related control methods. After discovering grape berry rot, fruit growers should remember not to panic, but should practically analyze the causes of grape berry rot and then take related control measures.