How Does Striga Infest Sorghum?

INTSORMIL Objective: (TO BE ADDED)

Introduction (DRAFT by C. Johnsen):

Several INTSORMIL principal investigators and projects contribute research on how to control Striga (USE FULL SCIENTIFIC NAME HERE?)—a weed that infests grain crops in Africa (AND CENTRAL AMERICA?) In this story, Alia Conley describes the devastation that Striga causes and how INTSORMIL scientists are helping farmers destroy the weed.(ADD PHOTO FROM VEIK-AFRICA.)

Story by Alia Conley

NOTE TO ADVERTISING CLASS: QUESTIONS IN CAPS AND PARENTHESES STILL NEED ANSWERS IN A FUTURE EDIT.

Farmers hope Striga, a parasitic plant, never attacks their crops.

Acting like a leech, Striga steals nutrients from a host plant. Striga is deadly because of

the aggressive, unique way it weakens crops directly, unlike other weeds, which compete with

crops only for space, water, sunlight and nutrients.

Also known as “witchweed,” Striga is one of the worst enemies for cereal crops such as

corn, millet, rice and sorghum, said Charles Wortmann, an INTSORMIL scientist at the

University of Nebraska-Lincoln. Striga works best in low-moisture climates and low soil-

fertility. The weed was once a problem in the U.S., but farmers in the U.S. have mostly

eradicated it, said Wortmann, who is also an associate professor of soil science at UNL. The

USDA Web site says only three states in the U.S. now have a form of Striga: North Carolina,

South Carolina and Florida.

But the situation is much different in Africa. (Q: WHY? IMPRACTICAL, TOO

COSTLY TO USE HERBICIDES?) where 20 to 95 percent of crops (Q: ALL CROPS? THIS

IS A HUGE SPREAD) are lost due to Striga. These crops are worth about $7 billion U.S.

dollars, the United Nations Development Program reports.

Striga spreads to sorghum crops through “contaminated seed and equipment, surface run-

off, eroded soil, wind, animals and people,” according to the African Agricultural Technology

Foundation. Each Striga plant can produce up to 50,000 seeds, which are tiny and easily

scattered. Striga infests about 100 million hectares (Q: ACRE EQUIV.?) of field crops in sub-

Saharan Africa, says a report by Gebisa Ejeta, an INTSORMIL scientist and professor of

agronomy at Purdue University.

Striga doesn’t strike right away. The seeds can stay inactive for up to 20 years, and

become active only when they sense that a sorghum root with plenty of moisture is close enough

to attack.

The battle starts once Striga attaches itself to a sorghum root. Striga sprouts roots, sticks

to the sorghum root and invades using a special tip of Striga’s root, called a haustorium. This

root end helps Striga suck nutrients and resources from sorghum, like a straw.

Sorghum dies from Striga because the crop wastes energy by providing the weed with

nutrients, according to the U.S. Department of Agriculture. Understandably, sorghum is less

productive, weaker and yields fewer seeds because Striga robs all the resources. Striga also

inhibits plant height and discolors sorghum.

“Most African countries have it. It’s common in Asia. It’s widely occurring in warmer

areas from 25 degrees latitude or closer to the equator,” Wortmann said.

Farmers can catch (Q: IS THIS WHAT YOU MEAN?) Striga early in its lifecycle. One

sign of Striga’s presence in a sorghum field is plants that fold and wither even though they are

receiving enough moisture. (Q: WHAT DO FARMERS DO THEN?) When farmers plant

sorghum year after year on the same land without rotating crop types—a system called mono-

cropping—Striga can attack more easily.

As Striga matures, yellow-green stems will emerge above ground four to seven weeks

after the first attack on the sorghum, according to the Pan African Striga Control Network. The

stems produce red flowers two weeks later. Numerous seed pods develop and hold 400-500

seeds. When seeds scatter, the cycle begins again.

“You can get quite high densities of Striga in the field,” Wortmann said. “The seed does

persist for a number of seasons and a number of years so it’s a problem that’s difficult to get rid

of once you have it.”

http://www.aatf-africa.org/userfiles/Striga-FAQ.pdf

http://www.africa.upenn.edu/eue_web/striga.htm

http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_phwitchweed.html

http://www.iita.org/cms/details/striga.pdf

http://plants.usda.gov/java/profile?symbol=STRIG

From CJ search:

From UN Development Program work at UNIV of Pennsylvania

http://www.africa.upenn.edu/eue_web/striga.htm

“The parasitic weed Striga exists as several species, the common economic ones being Striga hermonthica in East and West Africa and Striga asiatica occurring in South Africa, India, and to a small extent

Mid-Atlantic United States (Figures 1&3). Both attack sorghums, millet and maize, becoming the most devastating in the semi-arid tropics. The plants emerge from the soil adjacent to the host plant, produce many upright green stems with pink to white flowers. The third common species Striga gesneroides parasitises cowpeas and less often sweet potato (Figure 2) producing purple flowers and occurs largely in West Africa.”

“The prevalence of Striga soil infestation is steadily increasing as population pressures result in more continuous cultivation of cereal crops. In Ethiopia and elsewhere, land pressures cause farmers needing to feed their families to opt for continuous cropping of the higher yielding cereal crops without rotation or moving to other land. Again in the northern regions of Ethiopia, Striga is favoured by low soil fertility and soil moisture stress conditions (less shading by the poor growth of the host crop). This compounds the problem for the small-scale farmer who can least afford inputs on unproductive land. Infestation in some areas has reduced yields to the extent that abandonment and migration were necessary. Due to civil conflict, over-population, and droughts, farmer education and assistance programs have not been effectively applied in Ethiopia.”

Crop losses from on-farm studies and conservative estimates are reported (1,2,3) to be 40% for all Africa (US $7 billion), ranging from 20-95% in East Africa, 20-35% in Gambia, 10-90% with an average of 35% in Nigeria (US $250 million), and 60% in Sudan. A good method of estimating grain loss in an infested field is 3-4 kg/100 Striga plants/Ha for sorghum and 5-6 kg/100 Striga plants/Ha for maize, the lower number being used for fields or areas with less productive potential.