Identification of Common Diseases and Pests in Maize Seedling Stage and Scientific Control Methods
The period from jointing to emergence in maize is called the seedling stage, which is also the stage with the most pest species, the most concentrated outbreaks, and the most severe damage in the entire life of maize. So, what are the common diseases and pests in the maize seedling stage? How to control them scientifically?
I. What are the common diseases and pests in the maize seedling stage?
The main diseases in the maize seedling stage include maize root rot and seedling blight; the main pests are white grubs, thrips, and others.
II. How to scientifically control the common diseases and pests in the maize seedling stage?
1. Root rot
Symptoms: Maize root rot is a root rot caused by Pythium, mainly manifested as the mesocotyl and the entire root system gradually turning brown, softening, and rotting, with severely impeded root growth, stunted plants, yellowing leaves, and death of seedlings.
Control methods: In areas where root rot occurs severely, seed coating treatment of maize seeds with a fungicide-containing seed dressing agent should be adopted, or seeds should be treated with a fungicide before sowing. For root rot caused by Fusarium and Rhizoctonia, 75% chlorothalonil wettable powder, 50% carbendazim wettable powder, or 80% mancozeb wettable powder can be used to dress seeds at 0.4% of seed weight, or Vitavax seed dressing agent can be used directly for seed dressing. For Pythium root rot, oomycete-killing agents should be selected, such as 58% metalaxyl-mancozeb wettable powder, 64% oxadixyl-mancozeb wettable powder, or Lyuheng No. 1 seed dressing agent, used to dress seeds at 0.4% of seed weight.
2. Seedling blight
Symptoms: Symptoms generally begin to appear from emergence to the three-leaf stage, first causing the basal 1-2 leaves of maize seedlings to turn yellow, with leaf tips and leaf margins drying up, progressing gradually from the basal leaves upward, and further causing the central leaf to curl; in severe cases, the outer leaves of the plant dry up, the central leaf wilts and withers, and the plant dies.
Control methods: Apply chemicals promptly in the early stage of seedling blight. A 800-fold dilution of 70% thiophanate-methyl, or a 1000-fold dilution of 20% triadimefon, or a 3000-fold dilution of hymexazol can be used, sprayed twice consecutively (with an interval of about 7 days between applications); at the same time, Nongxi Shileisu, Blue Jingdian, Zhuanghan, or Liugao potassium dihydrogen phosphate high-efficiency nutritional regulators can be added to the spray to promote early seedling growth and enhance plant stress resistance and disease resistance, which can effectively prevent and control seedling blight.
3. White grubs
These insects like to feed on freshly sown seeds, roots, tubers, and seedlings; they are a worldwide soil-dwelling pest and cause great damage.
Control methods:
(1) Weed control
Plowing, sun-drying the soil, and removing weeds at field edges should be carried out early to reduce larvae and pupae in the soil.
(2) Capturing larvae
Every morning, before watering and replanting seedlings, pay attention to brushing aside the surface soil around damaged plants to find and capture larvae.
(3) Toxic soil control
Use 800 g of phoxim granules per mu mixed with 125-175 kg of dry fine soil, and broadcast it along the rows in the evening so that a protective belt is formed around the seedlings.
(4) Poison bait control
Use 0.5 kg of 90% trichlorfon crystals, add 2.5-5 kg of water, and spray it onto 50 kg of crushed, roasted, fragrant cottonseed cake, soybean cake, or rapeseed cake material. Scatter the poison bait around the rhizosphere of the seedlings.
(5) Chemical control
Use a 800-fold dilution of 90% trichlorfon for ground spraying, with a dosage of 75-100 kg per mu, or irrigate the seedlings, with 250-300 ml per plant.
4. Thrips
They mainly damage the underside of leaves, causing intermittent silvery-white stripes on the leaf underside, accompanied by small dark spots, while the corresponding parts on the upper leaf surface show yellow stripes. In severe cases, the leaf underside looks as if coated with a layer of silver powder, the distal half turns yellow and withers, and even the crop may be ruined.
Control methods:
(1) For maize fields adjacent to wheat fields, water and fertilizer management should be strengthened; when drought is observed, water and fertilize in a timely manner, which can reduce damage.
(2) In plots with high insect density or where a major outbreak is possible, promptly spray 20% carbosulfan emulsifiable concentrate or 10% imidacloprid wettable powder, 1.8% abamectin emulsifiable concentrate, 10% chlorfenapyr emulsifiable concentrate at 2000-fold dilution, 40% omethoate emulsifiable concentrate at 1500-fold dilution, or 25% Huifeng Kuaike emulsifiable concentrate at 1500—2000-fold dilution.
The quality of management during the maize seedling stage directly determines later maize production and has a crucial impact on quality and yield. Therefore, growers must do a good job in disease and pest control during the seedling stage.