What vegetable is the arrowhead, and how should its zonate leaf spot disease be prevented and controlled?

The arrowhead is a vegetable with a long history, appearing as early as the Tang Dynasty. The arrowhead is not only edible but also has certain medicinal value, being helpful for cooling the blood and stopping bleeding, relieving cough and treating strangury, dissipating nodules and detoxifying, and harmonizing the stomach and fortifying the intestines. In our country it is mainly grown in the provinces and regions south of the Yangtze River, so what are the prevention and control methods for zonate leaf spot disease occurring during the growth of the arrowhead?

I. What vegetable is the arrowhead?

The arrowhead is a vegetable unique to our country, suited to growing in water, taking root in the water towns south of the Yangtze River, with the Jiangsu-Zhejiang area as the main production region. Varieties include “Suzhou Yellow” and “Baoying Purple Round”, among others. The Pearl River basin, Yunnan and other places also produce arrowhead, with varieties differing from those of my hometown. The arrowhead growing in ponds stands elegantly, its leaves closely resembling a cut-open, shrunken taro leaf, so I had always understood it as a water taro, serving also as an ornamental.

The most classic way to cook arrowhead is none other than braised arrowhead with pork. For braising with pork, arrowhead is particular: the smaller the better, and the smaller, the more flavorful.

II. What are the prevention and control methods for zonate leaf spot disease in arrowhead?

1. Symptoms of arrowhead zonate leaf spot disease

Arrowhead zonate leaf spot disease is also a fungal disease. It mainly damages the leaves of the arrowhead, but it also does some harm to the leaf stalks. After zonate leaf spot disease develops, grayish-brown spots appear on the leaves, in elliptical, polygonal, and irregular shapes alike.

The pathogen overwinters in the soil as mycelium and conidiophores carried on diseased plant residues, or as mycelial masses attached to the diseased residues of arrowhead and its same-family weeds, and the seed corms can also carry the pathogen. After the weather turns warm the following year, conidia are produced and spread through airflow and rainwater, invading the plants and causing harm. The diseased parts continuously produce conidia for reinfection, causing the disease to keep spreading and worsening.

Fields with continuous cropping, excessive application of nitrogen fertilizer, application of undecomposed organic fertilizer, and excessively dense lotus-rhizome plant density with poor ventilation and light penetration suffer severe disease. High temperature and abundant rain, continuous overcast and rainy weather, insufficient sunlight, or frequent storms easily induce this disease; weak plant growth and field water temperature above 35°C also make it prone to occur.

2. What are the prevention and control methods for arrowhead zonate leaf spot disease?

(1) Select and plant disease-resistant varieties according to local conditions.

(2) Strengthen cultivation management. Use formula fertilization, and avoid excessive or over-application of nitrogen fertilizer; manage the water layer according to the needs of different growth stages, and especially pay attention to timely water replacement during the corm formation and swelling stage, avoiding long-term deep irrigation. Plant at a reasonable density, clear weeds from the field, and remove diseased plant residues from the field after harvest. Adopt soil testing and formula fertilization technology, appropriately increase the application of phosphorus and potassium fertilizers, strengthen field management, cultivate strong seedlings, and enhance plant disease resistance, which helps reduce the disease.

(3) Seed corm treatment. Select disease-free fields for seed retention, and carry out chemical treatment before planting; you may soak in a 1000-fold dilution of 40% triadimefon-carbendazim for 2 hours.

(4) Before winter, remove the diseased plant residues and surrounding weeds from the arrowhead field, deep plow and harrow, and broadcast 1500kg/hm of quicklime or apply chemicals for sterilization.

(5) For diseased plant residues that have already developed the disease, thoroughly remove them and burn them in a centralized manner or bury them deeply.