Weed Distribution in Corn Fields and the Best Control Methods, with a Comparison of Herbicide Effectiveness

According to the national weed survey results,corn fields have 22 families, 38 genera, and 43 species. The main weeds harming corn fields are: crabgrass, barnyardgrass, foxtail, goosegrass, redroot pigweed, purslane, Acalypha australis and Chenopodium (lamb's quarters), thistle (bull thistle and small thistle), field bindweed, Asiatic dayflower, etc., and the damage is greatest at the seedling stage, which can cause stunted corn plants, thin stalks and yellow leaves, severely affecting corn yield, with yield reductions of around 35%.

I. Distribution Regions and Characteristics of Weeds in Corn Fields in China

Corn cultivation in China is divided into six regions: the northern spring-sown corn region, the Huang-Huai-Hai summer-sown corn region, the northwest irrigated corn region, the southern hilly corn region, the southwest mountainous corn region, and the Qinghai-Tibet Plateau corn region.

Weed damage in corn fields is correspondingly divided into six regions: the northern corn field weed damage region, the Huang-Huai-Hai corn field weed damage region, the northwest corn field weed damage region, the Yangtze River basin corn field weed damage region, the South China corn field weed damage region, and the Yunnan-Guizhou-Sichuan corn field weed damage region.

II. A Comprehensive Review of Herbicides for Corn Fields

Using herbicides to control weeds means, on the one hand, killing the weeds, and on the other hand, it is essential to avoid causing damage to crops in the same field or even to subsequent crops. This places very high demands on the scientific use of herbicides!

1. Main classifications of herbicides for corn fields

(1) Corn herbicides are divided into three major categories by time of use:

The first category is post-planting pre-emergence herbicides, commonly known as soil-closure herbicides; such as acetochlor, acetochlor plus atrazine, metolachlor, etc.

The second category is early post-emergence herbicides, what farmers call small-weed herbicides (generally applied to stems and leaves when corn is at the 3-5 leaf stage, often systemic selective herbicides), such as nicosulfuron, atrazine, mesotrione (corn 3-8 leaf stage), 2,4-D, etc.

The third category is mid-to-late post-emergence herbicides, what farmers call large-weed herbicides (non-selective herbicides), such as paraquat, glyphosate, etc.

(2) Corn field herbicides are divided into three categories by treatment method:

1. Soil-closure herbicides - pre-emergence soil treatment

2. Stem and leaf treatment agents - post-emergence stem and leaf treatment

3. General-purpose pre- and post-emergence type - combining soil closure and stem and leaf treatment

Scientific weed control in corn

2. General-purpose pre- and post-emergence type - combining soil closure and stem and leaf treatment

3. Clear table of commonly used chemical weed control in corn fields: “match the herbicide to the weed”

4. Introduction to the main single-ingredient herbicides for corn fields

5. Comparison of weed control spectrum and effectiveness of commonly used corn herbicides

III. Control Strategies for Malignant Weeds in Corn Fields

1. Asiatic dayflower

(1) Bentazone: use 48% bentazone AS 100-200 ml/mu at the corn 4-6 leaf stage, as a stem and leaf treatment.

(2) Fluroxypyr + bentazone.

(3) Fluroxypyr + carfentrazone-ethyl.

(4) Hali (70.5% MCPA??carfentrazone WDG): 60 grams per mu after the corn 5-leaf stage.

2. Velvetleaf:

Optional agents include: flumetsulam, rimsulfuron, thifensulfuron-methyl, metribuzin, flumioxazin, bentazone, dicamba, mesotrione, halosulfuron-methyl, foramsulfuron, flazasulfuron, fluroxypyr.

3. Field bindweed:

Optional agents include: bentazone, fluroxypyr, 2,4-D isooctyl ester, MCPA, glyphosate, glufosinate.

4. Field horsetail:

Optional agents include: 2,4-D isooctyl ester, dicamba, dicamba (Banvel), glyphosate, flazasulfuron, flumetsulam.

5. Sowthistle, creeping thistle, bull thistle (bull thistle):

Optional agents include: bentazone, 2,4-D isooctyl ester, flazasulfuron.

6. Purple nutsedge:

(1) MCPA: 56% MCPA sodium salt SP 75-100 g/mu can be used, mixed with 30 kg of water per mu, and sprayed on the stems and leaves of purple nutsedge.

When applying, spray should be focused on the stems and leaves of purple nutsedge, and as little as possible should be sprayed onto the corn. The appropriate application period must be strictly observed, preferably at the corn 5-7 leaf stage, with the 5-6 leaf stage being best; it should not be too early or too late, otherwise phytotoxicity is likely to occur; if the application temperature is too high (above 32°C), phytotoxicity to corn is also likely to occur.

(2) 2,4-D butyl ester: 3-5 days after corn sowing, before emergence, use 72% 2,4-D butyl ester EC 50-100 ml per mu, mixed with about 35 kg of water, and spray evenly on the soil surface and weeds that have already emerged. It can also be used after corn emergence at the 4-5 leaf stage, using 72% 2,4-D butyl ester EC 40-65 ml per mu, mixed with about 35 kg of water, and sprayed on the stems and leaves of weeds.

(3) Bentazone: use 48% bentazone AS 100-200 ml/mu at the corn 4-6 leaf stage, as a stem and leaf treatment.

(4) Carfentrazone-ethyl: spray at the corn 3-5 leaf stage, using 50% carfentrazone-ethyl DF 5.3-8 g/mu, mixed with 30 kg of water; it can control broadleaf weeds such as speedwell, velvetleaf, redroot pigweed, Chenopodium, Kochia, cleavers, black nightshade, white mustard, wild sesame, redroot Chenopodium, etc., as well as sedges such as purple nutsedge.

Unlike hormone-type corn field herbicides such as MCPA and fluroxypyr, carfentrazone-ethyl has relatively little effect on corn aerial roots. However, when used on corn, high temperatures tend to cause phytotoxicity and have a certain effect on corn growth. When applying, it must be done before 8 a.m. on a sunny day, or after 4 p.m., and the temperature must not exceed 30°C.

(5) Hali (70.5% MCPA??carfentrazone WDG) at 60 grams per mu after the corn 5-leaf stage has good and fast control results on purple nutsedge and stubborn weeds that nicosulfuron and mesotrione cannot solve, such as field bindweed, creeping thistle, purslane, and sowthistle.

(6) 75% halosulfuron-methyl WDG: apply once at the corn post-emergence 3-5 leaf stage, when weeds are at the 3-5 leaf stage, with the best period being the 4-5 leaf stage. The formulation dosage is 75% WDG 45-60 grams/hectare, mixed with 15-30 liters of water.

It has relatively high herbicidal activity against some common broadleaf weeds in corn fields and sedge family weeds such as purple nutsedge, and is safe for most corn varieties. As a corn field herbicide, it should be used together with the safener MON13900.