Stenocarpella maydis

If the corn plant becomes infected soon after flowering, the husks appear bleached to straw color. Mycelial growth on corn ears typically begin at the base of the ear. In advanced stages of disease, this can result in a light-weight mummified ears attributed to the release of extracellular hydrolytic activities of acid protease, xylanases, and cellulases. During late season, this ascomycete on the plant can be recognized by the production of small raised, black fungal reproductive structures (pycnidia) on infected kernels, cob, husks, or stalks giving it an irregular feeling when touched. When infection happens several weeks after flowering, ears may be asymptomatic, with a possible brown discoloration, or seldom show mycelium between kernels. Some isolates may cause premature germination of the corn kernels. == Biology and epidemiology ==

S. maydis overwinters on diseased plant debris (husks, stalks). During wet conditions, flask-shaped pycnidia embedded on debris produces two-celled conidia. Diplodia ear rot takes place when conidia are spread via rain and wind into the plant during early silking until two to three weeks after silks start to senesce. Alternatively, conidia can penetrate husks, typically at the base of the ear. Fungal growth is most common during milk, dough and dent stages. Diplodia stalk rot takes place mainly in the crown, mesocotyl, roots, and less frequently on the nodes between the crown and the ear. For both diseases, points of entry are facilitated by pest (e.g. bird, insect) damage, predisposing the host. Earworm (Helicoverpa zea) damage at the ear shank is often associated with the disease. Corn Diplodia disease cycle Crop Protection Network == Worldwide incidence ==

The incidence of Diplodia ear and stalk rots is dependent of climatic factors. Epidemics have been associated with early droughts and late season rains. The incidence of infected corn in the field may range from 1-2% or as high as 75-80%. Belize, El Salvador, Honduras • South America: Argentina, Brazil, Colombia, Ecuador • European and Mediterranean region: Austria, Czech Republic, Italy, France, Russia • Africa: Kenya, Malawi, Nigeria, South Africa, Tanzania, Zaire, Zimbabwe • Asia: China (widespread), India (unconfirmed), Iran, Taiwan • Oceania: Australia (New South Wales) == Management ==

Cultural control • Timely planting: Alternate planting dates when possible. Spreading silk dates will reduce the risk of Diplodia infection. • Crop rotation: Alternate non-host crops at least one year out of corn to decrease the presence of the pathogen resting structures in subsequent seasons. • Irrigation timing: Overhead irrigation can splash disperse S. maydis spores from infected corn plants to adjacent healthy plants. • Grain drying and selection: Prior to storage, dry grain below 13-15% to halt mold growth. Prior to storage, clean dried grain by removing lighter, damaged kernels, cobs and fines. Routinely screen grain and store the most infected grain separately to reduce disease spread. Host resistance Corn hybrids vary in their susceptibility to S. maydis. Flint cultivars are more resistant than dent, and resistance breeding offers promise for control, however complete resistance (immunity) is not available. Further, resistance to insects can reduce damage and disease severity. Some experimental findings include: • Propiconazole and prothioconazole show promising results on a laboratory scale in reducing fungal growth under controlled conditions. In field applications, however, neither has shown successful Diplodia rot reduction. • Benomyl (Benlate) and mancozeb (Dithane M-45) have shown a degree of effectiveness in controlling S. maydis in the Nigerian Savanna. • A triazole product and a QoI strobilurin + triazole mix product tested by researchers at Purdue University did not consistently reduce disease severity. Biological control While not as commonly used as the previously described management strategies, several studies show promising results with a biocontrol approach. Examples follow: • Two Streptomyces sp. Isolates, designated DAUFPE 11470 and DAUFPE 14632, isolated from corn rhizosphere soil, significantly reduced S. maydis incidence by 93.2% and 92.3%, respectively. • Strains of Pseudomonas spp., P. fluorescens, Pantoea agglomerans, and Bacillus subtilis inhibited the development of this fungus for the production of compounds with antifungal activity. == Importance ==

S. maydis is capable of producing mycotoxins, but no case has been reported regarding Diplodia rot in the United States and Canada. However, there have been some mycotoxicoses (Diplodiosis) in South America and Africa due to this fungus. == See also ==