Évaluez l’état de santé de vos plants de maïs

Assess the Health of Your Corn Plants – The Farmers’ Bulletin

With the corn plants working hard to finish growing, there are issues that could jeopardize a successful end to the season. Corn stalk and leaf diseases can weaken the stalks and cause lodging. Other known stresses during the year could, in turn, cannibalize the plant into the kernels and weaken the corn stalk, making it susceptible to lodging and stalk rot.

Evaluations should be made between stages R5 (generally dentate grains) and R6 (maturity: maximum accumulation of dry matter, formation of a black spot at the base of the grains).

The Pest Alert Network (RAP) recommends two methods if there are problems. Fields with sandy soils, known for their compaction that limits the growth of roots or foliar problems present from the beginning of the season, should be prioritized.

push test

• Randomly select 20 plants from five well-distributed locations in the field, for a total of 100 plants.
• Push the top of the plant so that it is 15 to 20 cm (6 to 8 inches) from the vertical axis to see if the push causes lodging or not.
• Determine the percentage of weakened stems.

pinch test

• Randomly select 20 plants from five well-distributed locations in the field, for a total of 100 plants.
• Remove lower leaves and pinch stem above anchor roots. If she can easily
crushed, stem rot is likely. Symptoms can also be
observed by cutting the stem in half lengthwise.
• Determine the percentage of rotten stems.

Damage attributable to stem rots is mainly caused by three genera of fungi, viz. Cladosporium, Colletotrichum Where Giberella/Fusarium. The first two affect the transport of mineral elements in the plant, which can affect grain filling and make stems more prone to lodging. The gender fusarium It is one of the main producers of mycotoxins. Infected plants wilt and the leaves turn from light green to a dull grayish green, as if they have suffered from frost or drought. The inside of the temples will also show a change in appearance. They will appear frayed and their color can vary from white, pink, salmon, yellow to orange.

With respect to foliar diseases, the RAP indicates that the main foliar diseases of maize are currently common rust, dieback, kabatiellosis, and anthracnose. The latter can attack both the leaves and the stem.

The RAP also proposes to detect diseases that affect the ears since certain fungi can cause the development of mold in the ears. Evaluation should be done at the R5 and R6 stages, either in mid-September or a few weeks before harvest. You have to hand harvest at least 30 ears of corn from different random places in the field. Then the leaves that cover the cob should be removed to observe the presence of mold on the surface of the grains. If mold is observed, it is recommended that the grain be tested for the presence and levels of mycotoxins.

Depending on the case, an early harvest might be in order. In Ontario, it is recommended that a field with 10% of the ears affected by mold be harvested as soon as possible. If bird damage is evident (often at field edges), it is recommended to harvest damaged rows separately and, ideally, store and handle grain from these rows separately. Similarly, if a corn field has 10-15% rotten stalks or fallen plants, it is best to start harvest early and quickly to slow disease progression and potential mycotoxin production. Any additional cost of drying will be offset by greater ease of harvest and less loss in the field.

The drying of the grains must be carried out immediately after the harvest so that the humidity of the grains does not exceed 14%, because beyond this index, molds and mycotoxins continue to develop.

As for corn silage, once placed in the silo, the fungi must not grow and produce toxins, but for this the conditions must be completely anaerobic (absence of oxygen).

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