Disease Causes and Treatment Methods for Yellowing Leaves and Slow Growth in Rice at the Seedling Stage

Rice is the second largest food crop in our country, so achieving high rice yields is a matter of widespread concern. Because rice has weak resistance at the seedling stage, it is very prone to diseases. So what are the causes of these diseases? How can they be effectively treated?

1. Effects of nutrient deficiency

a. Nitrogen deficiency

Yellowing starts from the tip of the old leaves, then gradually extends downward to the central leaf, and finally the whole plant turns yellow-green. In severe cases, the leaf tips and leaf margins wither and turn yellow, the seedlings grow slowly, and from a distance the seedlings look entirely yellow. Quick-acting nitrogen fertilizers such as urea and ammonium bicarbonate should be applied promptly as a top dressing.

b. Potassium deficiency

When potassium fertilizer is insufficient, the plant is short and small, with few tillers, upright leaves, and new leaves that are dark green and lusterless. It develops from the old leaves upward, with rust-like spots appearing on the leaves, spreading from the leaf tip downward or from the leaf edge inward. In severe cases, the spots become large blotches or streaks, and the leaves die back in a reddish-brown color (also known as red blight), looking like they have been burned from a distance. When these symptoms appear, drain the water immediately, use intermittent irrigation, apply potassium fertilizer promptly as a top dressing, or spray potassium dihydrogen phosphate + Meizhouxing or seaweed acid.

c. Zinc deficiency

With zinc deficiency, the leaves first lose green and turn yellow-white in the midrib area, then yellow-red or red-brown spots or blotches appear, becoming red-brown and scorched, the leaves become narrower, and the veins become brittle and break easily. In severe cases, albino seedlings appear. Zinc sulfate or chelated zinc can be sprayed on the leaves as a remedy.

2. Yellowing caused by fertilizer burn or pesticide burn

Improper selection of fertilizers, excessive application rates, improper pesticide application, and re-spraying can also cause poisoning and yellowing, resulting in block-like and patchy yellowing of leaves. Sometimes the yellow leaves have scorched spots. When pesticide burn is severe, the leaves develop chlorotic or yellowed spots, or become scorched, dehydrated, and withered, and sometimes the entire plant dies. In the early stages, deep water can be immediately introduced into the field and changed 2~3 times, or clean water can be sprayed on the rice plants. Spraying Bihu or brassinolide + Meizhouxing or seaweed acid on the leaves can alleviate and reduce the severity of pesticide burn. This should be combined with the timely application of quick-acting fertilizers such as urea to help the plants recover quickly.

3. Yellowing caused by plant poisoning

a. Poisoning by reducing gases and hydrogen sulfide

The root system turns black, sometimes the soil smells of rotten eggs, and there are few white roots, which are thin. The old leaves at the base are yellow-brown, with scorched leaf tips. In severe cases, the old leaves die, leaving only 1~2 green new leaves at the top.

b. Organic acid poisoning

The root system shrinks and the epidermis peels off. There are few new roots, the leaves turn yellow, and sometimes wilting occurs. In severe cases, the lower leaves wither and die. Fields with toxic yellowing should also be drained immediately and the field dried to improve soil permeability, increase oxygen content, and promote root growth. In fields with excessive organic acids, quicklime or soil amendments should also be applied to neutralize soil acidity.

4. Yellowing caused by disease infection

a. Rice seedling blast

It mostly occurs before the 3-leaf stage. The base of the seedling turns black-brown, and the upper part appears yellow-brown or pale red. In severe cases, the leaves curl and the diseased seedlings die. Spray isoprothiolane or Fuji One or fenoxanil in a timely manner for control.

b. Damping-off

Leaves gradually turn yellow from the old leaves to the young leaves, the stem base becomes soft and rotted, breaks easily when pulled, and the whole plant dies back in a yellow-brown color. Pay attention to strengthening temperature management. In the early stages, spray metalaxyl + hymexazol or Runmiaoqing etc. + Meizhouxing or Anglibang for control.

c. Bacterial leaf blight

Generally, yellow-green or dark green spots first appear on the leaf tip or leaf margin, then extend along the veins into streaks and become gray-white. The boundary between the diseased part and the healthy part is distinct, and when humidity is high, yellow-brown “bacterial ooze” often appears on the lesions.

d. Rice bacterial leaf streak

It first appears as dark green, water-soaked, semi-transparent small spots, then forms pale yellow narrow streaks along the veins, oily and semi-transparent, with bacterial ooze overflowing under high humidity. In severe cases, multiple lesions can merge with each other, and the leaves die back in a red-brown color.

e. Bacterial foot rot

The central leaf wilts and curls, and some have already turned yellow and died, resembling the deadheart seedlings caused by stem borers, but there are no bore holes in the stem. The stem base often turns black and rots, with a foul odor, and the stem nodes become hard and brittle and break easily.

Summary of treatment for the above diseases: Bacterial leaf blight, bacterial leaf streak, and bacterial foot rot are all bacterial diseases. In the early stages, spray thiodiazole-copper or thiosen-copper or chlorobromoisocyanuric acid in a timely manner for control.

5. Yellowing caused by insect pests and leafhopper-borne virus infection

a. White-tip nematode disease

The upper part of the leaf tip shrinks and dies, appearing yellow-white or yellow-brown, and twists into a paper-spill shape. The key is to select disease-free seeds before sowing, or to use Jinzhongling or fenitrothion for seed soaking, which gives the best control. Once the disease occurs, spraying is less effective.

b. Rice yellow dwarf disease

The plant is stunted, with small leaves and clustered tillers, no mosaic pattern, and yellowing of the leaves and leaf sheaths. In severe cases, the plant dies.

c. Rice orange leaf disease

The leaf tips of the lower leaves yellow first, then the yellowing extends downward through the whole leaf and spreads upward, causing yellowing of all leaves on the plant. The plant is short, with few tillers, few new roots, and short, small, upright leaves. After tillering, diseased plants die easily.

d. Yellow dwarf disease

Yellowing starts from the tip of the top leaf and the leaf below it and moves downward. Diseased plants are notably stunted, do not tiller, have few and short roots, and the diseased leaves lie flat or even droop. In severe cases, the plant dies.

Summary of treatment for the above diseases caused by leafhopper-borne viruses: Yellow dwarf disease, yellow dwarf disease, and orange leaf disease are all caused by leafhopper transmission. Paying attention to controlling leafhoppers routinely can effectively prevent their occurrence. When they occur in the field, pull out and destroy the affected plants promptly, and spray isoprocarb + Aitailing or ningnanmycin + Bihu for control.

6. Yellowing caused by virus transmission by the small brown planthopper

a. Downy mildew

The plant is stunted, the leaves are chlorotic and mosaic-like, the spots are yellow-white, and sometimes the central leaf yellows and twists. In severe cases, the whole plant yellows and dies. In the early stages, spray metalaxyl mancozeb or cymoxanil zinc or propamocarb in a timely manner for control.

b. Rice stripe disease

The central leaf is affected, with intermittent yellow-green or yellow-white streaks along the veins. As the lesions enlarge, half or most of the diseased leaf turns yellow-white, while the rest still shows chlorotic stripes. The plant is not obviously stunted and has few tillers. Tall varieties bend and droop in a paper-spill shape, and in severe cases the plant dies.

Summary of treatment for diseases transmitted by the small brown planthopper carrying viruses: These are caused by virus transmission by the small brown planthopper. Pay attention to controlling the small brown planthopper routinely, especially in seedling fields. When they occur in the field, promptly spray Bingduling or Aitailing + Bihu or brassinolide + thiamethoxam or sulfoxaflor for control.

7. Effects of insect pests

a. Thrips

After thrips damage the leaves, yellow-white small spots or micropores appear, the leaf tips wither and yellow and shrink lengthwise, and in severe cases patches of seedlings turn yellow and red, as if burned by fire. Promptly use clothianidin or carbosulfan or imidacloprid for control, and at the same time pay attention to strengthening water and fertilizer management.

Final summary: Pay attention to soil testing and formula fertilization, do not use undecomposed organic fertilizer, do not apply excessive nitrogen fertilizer, plant at a reasonable density, and do not transplant too deeply or allow excessive water accumulation in the field. Use pesticides scientifically and reasonably, carry out seed dressing or seed soaking before sowing, and cultivate robust plants. Routinely control virus-carrying transmission pests such as the small brown planthopper and leafhoppers in seedling fields and fields, which can effectively reduce and prevent leaf yellowing caused by the above reasons.