A Cornucopia of Disease in Southeast Asia

I sometimes find such healthy grass that I have little disease to write about, but this week was an exceptional one. I went from Kanchanaburi to Bangkok, Singapore, and Da Nang, seeing a number of grasses and on them an assortment of pathogens. Click the thumbnails for a full-size image and description.

If there were an award for diseases, seashore paspalum would win this week, with two different unidentified diseases and slime mold and dollar spot, with a bonus for some extraordinary drought stress. In the image below, there is an unidentified patch disease and dollar spot on a seashore paspalum fairway in Bangkok. And you can see the drought stress in the drain lines going to the catch basin in the background. But wait! Can you see the patch of Zoysia matrella in the center-left of the photo? The Zoysia matrella that is free of disease and doesn't have the drought stress of the paspalum even though it is growing in the drain line? Seashore paspalum does not grow well at all in Southeast Asia in areas of low soil moisture content.

Seashore paspalum grows wild in tidal swamps and in intertidal zones. Which is exactly where I found it growing on the beach at Da Nang (below), in its natural environment, and free of diseases. But come in from the beach a short distance, where the high tide does not reach, and I found wiry Zoysia matrella growing in the dunes.

There was brown patch on bermudagrass at Vietnam and bermudagrass white leaf, which I think is the most unsightly disease, on bermudagrass at Singapore and Vietnam.

Most of the diseases, you notice, were on seashore paspalum and bermudagrass. I saw two types of broadleaf carpetgrass this week, both free of any disease. This grass thrives in the umbrageous conditions so ubiquitous in tropical Southeast Asia, as does zoysiagrass.

And for those more interested in cool-season grasses, you probably read with some interest the post from Dr. Kerns and Dr. Soldat a few weeks ago about managing potassium on cool-season turf. I'm fascinated by the Park Grass experiment and its results showing that potassium and lime application cause a proliferation of dandelions and other weeds, and the most recent issue of the Green Section Record has an article with some insights into that experiment and how the results "carry lessons of high importance in the growing of golf turf."

When is Scalping a Good Thing?

When is scalping a good thing? When it teaches us something useful. In parks and commercial landscapes in Southeast Asia, the normal maintenance for broadleaf carpetgrass (Axonopus compressus) or manilagrass (Zoysia matrella) involves infrequent mowing at low mowing heights. Grass may be allowed to grow to a height of 30 to 50 mm (1.25 to 2 inches) or higher and then it will be scalped down with a string trimmer nearly to ground level, to something less than 12 mm (0.5 inch). See the video below from a resort at Pai in northern Thailand. I was here recently for some belletristic work.

This scalping would seem like rather poor maintenance, but I suggest that the scalping is a good thing in that it teaches us something about these grass species and their adaptation to low light conditions. Broadleaf carpetgrass and manilagrass tolerate (or even thrive with) this regular scalping, while seashore paspalum and bermudagrass do not. Sure, the average turf quality would be better if the grass was mowed frequently rather than scalped, but this removal of 70 to 90% of the leaf area at one mowing produces a good turf for many resorts and parks and lawns and roadsides in this part of the world.

I like to think about scalping as applying artificial shade to the grass. Shade reduces the amount of light available for photosynthesis. And so does scalping, by removing nearly all the leaves. The grasses that can tolerate scalping in Southeast Asia are also those that are well-adapted to this growing environment. And these are also the grasses that have minimal disease problems and thrive on golf courses. Golf courses planted to bermudagrass or seashore paspalum generally have more disease pressure, whether that be bermudagrass decline or dollar spot or an assortment of leaf spots and other maladies.

Now consider broadleaf carpetgrass (above, on a fairway mowed at 8 mm [0.3 inch] in Hong Kong) and manilagrass, by comparison. These grasses can be scalped. And they are relatively disease-free. Other than fairy ring, I have never seen any disease on broadleaf carpetgrass anywhere in tropical Southeast Asia. In sub-tropical Asia it may suffer from large patch during the short winters. That’s all. The only diseases I have seen on manilagrass in tropical Southeast Asia are fairy ring and curvularia leaf blight. Just those two. Ever. The curvularia leaf blight (see below) only occurs during the rainy season and is relatively easy to control.

Mites, a Corpse Plant, and Native Grasses

I was at Bangladesh last week and I saw something that, in years of turfgrass work in Asia, and hundreds of visits to golf courses and other turfgrass sites, I had not seen before. At first, I thought this was a broadleaf weed invading a bermudagrass fairway. From above, this looks a bit like Mimosa pudica, one of my favorite weeds.

In fact, this is bermudagrass, but it is infested with mites, causing a change in the growth habit and drastically shortened internodes. For a closer look, see the image below, with both normal growth and modified growth on the same stolon.

That is definitely not Mimosa pudica! I saw bermudagrass mite damage at Hawaii this spring but the stunting was not so severe and the characteristic "witch's broom" appearance of the mite-infested turf, at Hawaii, was more of a broccoli or cauliflower shape, rather than this compressed and narrow appearance as noticed in Dhaka and Chittagong. My friend Storm Lupier sent me photos showing very similar symptoms on bermudagrass in the Seychelles. And there was similar damage on zoysiagrass turf at Dhaka as well. The two photos above are bermudagrass; the image below is zoysiagrass.

If you have a problem with mites at your course, consult with a local expert or follow the advice in this publication from the University of Florida.

I saw a bit of fairy ring on broadleaf carpetgrass (Axonopus compressus) at Bangladesh and on hybrid bermudagrass at Indonesia this week. The fairy ring disease profile at TurfFiles from NC State summarizes the recommended control measures for fairy ring.

You may be aware of the corpse plant (Amorphophallus titanum -- you can translate that yourself); I have not seen one, and being at Bogor recently, I went to look for one at the Bogor Botanical Gardens. These extensive gardens are 193 years old and have over 15,000 plant species and thousands of orchid varieties. Alas, I did not see a corpse plant in bloom, but I did see pulchritudinous acres of broadleaf carpetgrass, growing in full sun and in the shade of massive tropical trees, and the grass was completely free of diseases. In Southeast Asia, the grasses that grow as native plants here are generally free of diseases when maintained as turfgrass; these grasses are broadleaf carpetgrass (Axonopus compressus) and manilagrass (Zoysia matrella). Sod farms near Bangkok can produce a crop of manilagrass in six weeks using no herbicides, no fungicides, and very little mechanized equipment. See how in this short video: