Corn top rot is a new disease in corn production in recent years. It has been on the rise in recent years, and the damage has become more serious. It is mainly caused by Fusarium oxysporum in the soil. The disease can occur in the whole growth period of corn, but it is most obvious before and after heading (summer corn is generally from late July to early August).
Due to recent weather changes, or drought or phlegm, it is easy to cause a large area of ​​top rot, because its symptoms are complex and diverse, and some symptoms are similar to other diseases and insect pests and deficiencies of corn, and should be carefully compared in diagnosis. Detailed identification, timely prevention!
First, the symptoms
Field observations revealed that the heart leaves protruding from the bell mouth were chlorotic and yellowish, and some of the leaf margins became thin and white. As the disease progressed, brown rot appeared on the top of the leaf, and the decayed part expanded downward along the edge of the tip.
The leaves on the top of the plant with early onset and heavy onset are tightly wrapped and adhered together, showing a "shooting tip" shape, which is prone to rot and the tassel cannot protrude. According to relevant information, the symptoms of corn top rot are complex and diverse, and other symptoms are as follows:
1, the leaf edge is missing. The base or edge of the susceptible leaf has a knife-shaped nick, and the leaf margin and the top chlorotic are yellow-colored. In severe cases, one half of the leaf or the whole leaf falls off, leaving only the midrib of the leaf and a small amount of mesophyll tissue remaining on the midrib.
2, the blade is dead. The edge of the base of the blade is brown and rotted, and the blade sometimes has a tearing shape or a broken leaf shape. In severe cases, the tip of the top 4 to 5 leaves or the whole leaf die.
3. Twisted wrap type. The top blade is curled into an upright long whip, and some are wrapped by other leaves to form a bow when forming a whip. Some of the top leaves are twisted and entangled and cannot be stretched, and the tangled leaves are often torn or wrinkled. Shrink.
4, leaf sheath, stem rot type. The diseased plants with brown rot of the base of the ear node often rot in the sheath of the leaf sheath and the stalk. The inner side of the sheath and the stalk cortex of the stalk are rust-colored, and the stem is cut open, and the internal vascular bundle and stem are visible. There are brown spots or short strips of discoloration, some appear hollow, endogenous white or pink mold, and it is easy to fold when windy.
5, elbow type. The leaf base and stem of the ear are yellow, the stem and sheath tissues are softened, and the top of the plant is inclined to one side.
6, the top leaf cluster type. Some varieties have clustered apex and erect after the disease.
7, abortive or empty stalk type. Lightly susceptible plants can be sturdy, but the ears are small and the seeds are less; the severe females and tassels are aborted, deformed and unable to head, or form empty stalks.
Second, the cause of the disease
Corn top rot can be divided into fungal type and bacterial type, and the disease is likely to occur in the flare stage. Especially in high temperature, rainy, strong light climate conditions, it is easy to damage the young tissue at the top of the blade, resulting in rapid invasion of bacteria. In addition, the daily spit water and high temperature climate of the corn are beneficial to the large number of bacteria, causing a large amount of rot at the top of the blade. . In general, the incidence of corn rot in low-lying plots and soil-heavy plots is heavy.
1. Fusarium top rot. Symptoms are manifested in the period from the seedling stage to the adult stage of the corn. The heart leaves rot and dry from the base of the leaves, tightly wrapping the inner heart leaves so that they cannot be unfolded and whip-likely twisted; or the base of the heart leaves is longitudinally cracked, the leaves are deformed, shrunken or distortion.
The plants are often dwarfed, and the base of the stem can be seen to be longitudinally cracked and have brown lesions; the severely ill plants are not strong or the ears are small and even dying. Pathogenic bacteria generally invade from young tissues such as wounds or stem nodes and heart leaves, and the damage of insect pests, especially thrips and aphids, can aggravate the occurrence of diseases.
2, bacterial top rot. It can happen before the corn is taken. The typical symptoms are that the heart leaves are gray-green, water-deficient, wilted, and formed into dead seedlings or clusters; the base of the leaves is water-soaked and rotted, the lesions are irregular, brown or yellow-brown, and the rot has or has no special odor and mucus.
In severe cases, the whole heart can be pulled out by hand, and the heart of the light disease plant can not be distorted. High temperature and high humidity are conducive to disease prevalence, and wounds caused by pests or other causes facilitate the invasion of germs. Mostly after the rain or after irrigation in the field, the plots with low or poor drainage are heavier.
Third, prevention and treatment methods
1. Make full use of sunny weather, speed up the process of shovel, remove moisture and heat, eliminate weeds, improve seedling quality and enhance disease resistance.
2, timely topdressing, corn fertility process into the big bell mouth period, it is necessary to quickly apply nitrogen fertilizer to the corn, especially for the heavier plots to do better early fattening work. At the same time, it is necessary to spray the micro-fertilizer on the foliar surface, and spray the functional fertilizer of Prideon fish protein in the United States to promote early seedling growth, supplement nutrients and improve the resistance to stress.
3, chemical control, to achieve early detection, early medication. In the early stage of the disease, 58% metalaxyl · manganese zinc wettable powder 600 times liquid, or 70% methyl thiophanate 700 times liquid, or 50% carbendazim WP 500 times liquid, plus 72% agricultural streptomycin water Solvent 2500 times solution, mixed spray control.
The key point of application should be directed at the heart of the diseased plant. The diseased plant should increase the amount of liquid, and control it 1 or 2 times according to the incidence. For the leaves that are stuck together, the blade should be grasped with a knife tip or an awl to pick up the adhered leaves to promote the growth of the apex and the normal development of the tassel.
Under the conditions of ventilation and sun exposure, the diseased tissues will quickly dry up and effectively control the development of the disease. When the disease is late, the plants have been headed, and it is difficult to spray in the field. At this time, the control measures for spraying are not recommended.
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