Drought-stressed corn may exhibit poor stalk strength

By TONY NYE

nye.1@osu.edu

The 2012 har­vest is in full swing and if weather holds, this could be a har­vest com­pleted ear­lier than nor­mal. Yields will vary and be all over the board due to the exces­sive heat and very dry con­di­tions at many crit­i­cal times through­out the grow­ing season.

Ohio State Uni­ver­sity agron­omy spe­cial­ists, Peter Thomi­son and Pierce Paul, warn pro­duc­ers that the drought con­di­tions expe­ri­enced dur­ing grain fill often increase the poten­tial for stalk rot and lodg­ing prob­lems in corn. When stalk rot occurs late in the sea­son as it often does, it may have lit­tle or no direct effect on yield. How­ever, stalk lodg­ing, which results from stalk rot, can have such an impact on har­vest losses that many plant pathol­o­gists con­sider stalk rots to be the most sig­nif­i­cant yield lim­it­ing dis­ease of corn.

For a corn plant to remain healthy and free of stalk rot, the plant must pro­duce enough car­bo­hy­drates by pho­to­syn­the­sis to keep root cells and pith cells in the stalk alive and enough to meet demands for grain fill. When corn is sub­jected to drought stress dur­ing grain fill, pho­to­syn­thetic activ­ity is reduced. As a result, the car­bo­hy­drate lev­els avail­able for the devel­op­ing ear are insuf­fi­cient. The corn plant responds to this sit­u­a­tion by remov­ing car­bo­hy­drates from the leaves, stalk and roots to the devel­op­ing ear. While this “can­ni­bal­iza­tion” process ensures a sup­ply of car­bo­hy­drates for the devel­op­ing ear, the removal of car­bo­hy­drates results in pre­ma­ture death of pith cells in the stalk and root tis­sues, which pre­dis­poses plants to root and stalk infec­tion by fungi. As plants near matu­rity, this removal of nutri­ents from the stalk to the devel­op­ing grain results in a rapid dete­ri­o­ra­tion of the lower por­tion of corn plants in drought stressed fields with lower leaves appear­ing to be nitro­gen stressed, brown and/or dead.

Other plant stresses which increase the like­li­hood of stalk rot prob­lems include: loss of leaf tis­sue due to foliar dis­eases (such as gray leaf spot or north­ern corn leaf blight), insects, or hail; injury to the root sys­tem by insects or chem­i­cals; high lev­els of nitro­gen in rela­tion to potas­sium; com­pacted or sat­u­rated soils restrict­ing root growth (recent flood­ing); and high plant populations.

Thomi­son and Paul note that most hybrids do not begin to show stalk rot symp­toms until shortly before phys­i­o­log­i­cal matu­rity. It is dif­fi­cult to dis­tin­guish between stalk rots caused by dif­fer­ent fungi because two or more fungi may be involved. Sim­i­larly, cer­tain insects such as Euro­pean corn borer often act in con­cert with fun­gal pathogens to cause stalk rot. Although a num­ber of dif­fer­ent fun­gal pathogens cause stalk rots, the three most impor­tant in Ohio are Gib­berella, Col­lec­totrichum (anthrac­nose) and Fusar­ium. For more infor­ma­tion on stalk rot in corn, con­sult the OSU Plant Pathol­ogy web­site “Ohio Field Crop Dis­eases” (www.oardc.ohio-state.edu/ohiofieldcropdisease/) for more details and pic­tures of the dis­ease symp­toms asso­ci­ated with these pathogens.

The pres­ence of stalk rots in corn may not always result in stalk lodg­ing, espe­cially if the affected crop is har­vested promptly. It’s not uncom­mon to walk corn fields where nearly every plant is upright yet nearly every plant is also show­ing stalk rot symp­toms. Many hybrids have excel­lent rind strength, which con­tributes to plant stand­abil­ity even when the inter­nal plant tis­sue has rot­ted or started to rot. How­ever, strong rinds will not pre­vent lodg­ing if har­vest is delayed and the crop is sub­jected to weath­er­ing, e.g. strong winds and heavy rains.

A symp­tom com­mon to all stalk rots is the dete­ri­o­ra­tion of the inner stalk tis­sues so that one or more of the inner nodes can eas­ily be com­pressed when squeez­ing the stalk between thumb and fin­ger. Thomi­son and Paul sug­gest it is pos­si­ble by using this “squeeze test” to assess poten­tial lodg­ing if har­vest­ing is not done promptly. The “push” test is another way to pre­dict lodg­ing. Push the stalks at the ear level, 6 to 8 inches from the ver­ti­cal. If the stalk breaks between the ear and the low­est node, stalk rot is usu­ally present. To min­i­mize losses from stalk lodg­ing, avoid har­vest delays. Iden­tify fields which are at great­est risk and har­vest these fields first. Fields which expe­ri­enced drought stress, defo­li­a­tion due to hail, foliar dis­ease injury, etc. would be prime can­di­dates for early harvest.

(Tony Nye is the Agri­cul­ture and Nat­ural Resources Edu­ca­tor for the OSU Exten­sion, Clin­ton County.)

Posted by Tina Murdock on Oct 3 2012. You can follow any responses to this entry through the RSS Feed. Both comments and pings are currently closed.