What causes rotten grapes? Causes and control measures
Growers who have planted grapes usually encounter the phenomenon of rotten grapes, especially in the middle and late stages of grape growing. Once the fruit rots, it seriously affects grape yield and variety quality, bringing huge economic losses to farmers. Therefore, Qinnong Network has brought you an analysis of the causes of rotten grapes and how to prevent and control the phenomenon of rotten grapes.
I. Causes of the disease
1. Pathogen infection. The diseases that cause rotten grapes mainly include white rot and anthracnose, and in special years there is also black rot. White rot and black rot not only cause rotten fruit and rotten clusters, but also infect grape vines and form brown lesions. In severe cases, diseased branches and leaves wither and die, and the tree vigor weakens, affecting the yield and quality of the fruit in that year and the next 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. At this time, the climate characteristics of high temperature, high humidity and frequent rain easily cause major epidemics 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 branches and vines. Coupled with abundant rain and stuffy air, a microclimate of high temperature and high humidity is easily formed inside the trellis. If mechanical wounds are further caused by storms, hail, sunburn, fruit cracking, or birds and insects, the epidemic of “rotten fruit disease” will be aggravated and secondary diseases will be triggered.
4. Weak tree vigor. The following factors can 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, and delayed vine tying, pinching, shoot thinning, and cluster straightening, resulting in poor nutrient supply during the fruit growing period; too many ineffective branches and leaves, causing excessive ineffective consumption; too much fruit hanging on the tree, and weeds growing densely under the trellis; severe pests and diseases, etc.
II. Control measures
1. Change trellis arm training to small shed trellis training to create a microclimate unfavorable for disease occurrence. Small shed trellises, single cordon or double cordon pruning, and medium and 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 required to be about 30%. During the growing season, summer pruning, vine tying, shoot thinning, pinching, and fruit cluster spreading should be done in time, so that the fruit clusters hang under the “dappled shade” of the trellis surface, avoiding sunscald 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 trenching in alternate years and alternate rows, preferably chicken manure, with an appropriate amount of phosphorus and potassium fertilizer. The temperature during this period is relatively high, which not only favors the decomposition of organic fertilizer, but also gives the leaves strong photosynthetic capacity, enabling effective use of nutrients. In the later stage of grape growth, a 2%~3% potassium dihydrogen phosphate solution can also be sprayed along with pesticide application, which can significantly enhance tree vigor and reduce the occurrence of “rotten fruit.” Plant growth regulators can be sprayed according to the plant growth condition 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 moisture. For clayey soil, soil improvement should also be noted to enhance the air permeability of the root zone soil. Attention should be paid to raising the fruiting position, and fruit clusters should be kept as absent as possible at 40~50 cm above the ground to reduce the chance of pathogen infection.
3. Remove sources of inoculum. After autumn, before the vines are taken down from the trellis, remove diseased residues from the orchard and burn them in a centralized manner. Before burying the vines for winter protection in autumn and after they emerge in spring, spray 50~100 times dilution of Solibar or 3~5 degrees Baume lime sulfur mixture + 300 times dilution of sodium pentachlorophenate to remove sources of inoculum. During the growing season, promptly remove diseased leaves, diseased fruit and diseased vines, and bury them deeply in a centralized manner.
4. Strengthen trellis management. Pay attention to timely vine tying and pinching to maintain ventilation and light penetration within the trellis. Determine the yield according to the plant growth condition. Generally, the yield of a mature orchard should be controlled at 2,500~3,500 kg per 667 sq m.
5. Chemical control. For infected vineyards, before the tree buds, spray the tree body or the ground with 2 degrees Baume 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, once every 10~15 days throughout the growing season, but note to alternate and rotate the pesticides.
For orchards with severe disease in the previous year, before disease occurrence, spray 500~600 times dilution of thiram or 500~600 times dilution of 50% carbendazim under the trellis to eliminate the pathogens 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 note 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 summary collected and organized by Qinnong Network on the causes of rotten apples and related control methods. After growers discover rotten grapes, they must remember not to panic, but should practically analyze the causes of the rotten grapes, and then take relevant control measures.