By Dave Nanda, Ph.D., Seed Genetics Direct director of genetics
With all the bad news about the coronavirus this year, we need a miracle. It is really a miracle of nature that a puny little seedling can grow into a big, tall corn plant within a couple of months. The most crucial time in the life of a corn plant is the seedling stage. If we understand how our crops grow, we can do a better job of meeting their needs and improve the odds for getting higher yields. Let’s look at what happens as the young corn plants develop.
Stage V1 to V2 — corn seedlings need 110 to 120 growing degrees to germinate and emerge. The seedlings emerge when coleoptile, the spear-like leaf, pierces thru the ground. First and second leaves develop six to seven days after the seedlings emerge. The first roots start to supply water and nutrients to the young seedlings. Roots are very small and the availability of fertilizer close to the roots at this stage is very helpful in stimulating early growth, just like a baby needs milk soon after birth.
Stage V3 to V4 — about two weeks after emergence, the third leaf starts to develop. Seedling roots stop at this stage and the secondary roots start growing. These become a part of the permanent root system of the plant. At V3-V4 stage, make sure that weeds are under control. Apply post-emergence herbicides, if necessary. Even small weeds can affect yield. The growing point stays below ground for three to four weeks and is protected from frost or insects on the surface. Don’t cultivate too close to the plant after this stage because the roots may be damaged. Freeze at this stage may hurt the leaves, but the growing point is not destroyed since it is below ground. Don’t start thinking about replanting at this stage. The nodal roots are growing fast and start taking over the responsibility of gathering water and nutrients for the whole plant. Root hairs also start growing at this stage.
Stage V5 — four nodes develop below the ground. Generally, the first node above ground is the fifth node. Even at this early stage, leaf and ear shoots are starting to develop. Take care of the young plants and you will have productive healthy adults and a good crop.
At seedling emergence, young plants face many hurdles such as nutrient deficiencies, seedling diseases like Pythium and Stewart’s bacterial blight, slugs and insects like black cutworms. Corn rootworm beetle larvae attack the roots during June and early July. In a wet spring, we need to watch out for slimy little creatures like slugs. They appear harmless but can cause considerable damage, especially in low-lying areas of the fields.
Stage V6-V8 — if you are going to apply additional nitrogen, be sure to sidedress with before the plants are too tall. Check for deficiency of nutrients like sulfur as well as zinc, magnesium and other micronutrients. If you take care of the seedlings, they will reward you well when they grow up.
There are several potential seedling diseases which could interfere with germination and successful emergence.
Corn seedling blights
Cool and wet conditions are ideal for fungal seedling blights. Corn that was planted earlier in some areas or in no-till ground is more susceptible to these diseases.
Specific fungi: Pythium, fusarium and rhizoctonia
The pathogens that infect corn seedlings are species of Pythium, Fusarium and Rhizoctonia. These fungi over-winter in the soil or plant debris. These fungi can infect a substantial portion of the developing root system. Other fungi that can cause seedling blights includes Gibberella, Diplodia and Penicllum.
The best prevention occurs before you plant. Select and plant high-quality seed treated with fungicides, and plant when soil temperatures are above 50 degrees F and you should have a good plant stand to get this miracle of nature off to a good start in 2020.