White clover, the savior of overgrown melon vines, reduces viral disease by 20% and fertilizes the soil

The moment you mention "mad vine" (feng cong), you could say it is the nightmare of every farmer who grows cucurbits, because usually they are not quite sure why the plants got infected, and as soon as they accidentally catch it, a whole swath dies off. The worst part is that, to date, there is no medicine that can cure it, which makes people turn pale at the mere mention of it!

"That is exactly what happened to me the year before last. Almost the whole field was completely wiped out, with no harvest at all. Even if any fruit set, it was just a tiny little one, and there was simply no way to sell it. I lost over a hundred thousand, it was really miserable!" said Huang Xingsheng, a melon farmer in Ruisui with 15 years of organic pumpkin experience. Even though he is full of growing experience from head to toe, when he runs into mad vine he is just as helpless, able only to shake his head and sigh again and again.

Viral infection of the "mad vine" terminal disease, once infected there is no cure

What farmers call "mad vine," "anti-mad," and "going mad" is in fact crops infected with a viral disease, and farmers especially often make viral diseases hard to bring under control because of continuous cropping.

"Once this disease is caught, you could say there is no cure. 'Mad vine' is really so brazen!" Huang Xingsheng recalled his previous painful experience, shook his head, and said helplessly, "There is no way. Farming really is completely a matter of luck!" He said that when the temperature is normal it is still all right, but if there is suddenly a stretch of alternating cold and hot weather, it is very easy for toxin disease to arise. As soon as a plant is infected even a little, it must be pulled out immediately, with absolutely no room for negotiation, otherwise the losses will only be worse.

So for "mad vine" infected by a virus, all farmers can do is try their best to prevent it, and to date there is still a lack of fully effective control agents. For farmers, if they are unlucky enough to get infected, one or two days later the whole melon field may immediately fall, and it can almost be described as a "terminal disease" or "no cure," which is truly miserable!

The silverleaf whitefly spreads plant viruses, causing plants to "go mad." "In fact, plant viruses themselves have no means of movement; they are all transmitted by disease-vector insects." Cai Weian, assistant researcher at the Hualien District Agricultural Research and Extension Station, pointed out that most of Taiwan's cucurbit viruses are transmitted by the silverleaf whitefly, aphids, and thrips, and among these the silverleaf whitefly's spread is the most serious. Although the silverleaf whitefly is small, its migration and reproduction ability is very strong. It feeds on tender leaves by piercing and sucking, and at the same time transmits the virus. As long as the silverleaf whitefly carries the virus on its body, even if the number is not large, it will spread it very quickly. And when crops are attacked by the virus, what farmers can usually do is only painfully remove the diseased plants, because the early prevention and treatment window has already been missed, and at the same time there is no specific effective medicine to inhibit it. Normally, most farmers use insecticides to control pests, "but this not only increases costs, it also only breeds more pesticide-resistant pests." Therefore, Cai Weian suggests that in addition to chemical control of disease-vector insects, other control methods should be combined to increase the overall control rate. Moreover, if it is organic, insecticides simply cannot be used at all!

White clover becomes a savior, reducing the chance of toxin disease by twenty percent

So when Huang Xingsheng's pumpkin was infected with toxin disease two years ago, he hurriedly contacted the Hualien District Agricultural Research and Extension Station, hoping to get assistance. Chen Renfang, associate researcher studying crop diseases, and assistant researcher Cai Weian then brought organic control materials down to Ruisui, hoping the new control method could prevent such regrettable incidents from happening again. "The two of them are very serious; they come down on every visit, from sowing all the way until harvest!" Huang Xingsheng praised, and what made him even happier was that they also brought a brand-new field cover crop — white clover, which was being used in Taiwan to reduce the harm of disease-vector insects for the first time. The method is very simple: first scatter white clover seed in the ridges and furrows, then lay down plastic sheeting, and afterward plant the pumpkin seedlings. The main point is to use white clover to attract the disease-vector insects to settle, thereby substantially reducing the chance of harm to the pumpkin seedlings. "There was an effect in the first year!" Huang Xingsheng described it. It was not that he saw the insects all running into the white clover, because the insects are so small they are almost invisible, but rather he noticed that the situation of them sucking the tender shoots of the melon leaves had decreased, and he could also clearly feel that the pumpkin's growth was better. "It reduced the chance of toxin disease by about twenty percent." He estimated. The probability of pests preferring white clover under the same grass cultivation was obtained by comparison with the grass cultivation beside it. In order to make a mutual comparison, Huang Xingsheng divided the field into two zones: half of the ridges were planted with white clover; the other half used traditional grass cultivation. By comparison, on the white clover side, the health of the pumpkin leaves and the reduction in viral harm were clearly felt. "I think the insects should also stop on the grass of the grass cultivation, but perhaps they like the taste of white clover more, so more pests are attracted over, and the effect is better than ordinary grass cultivation." Regarding white clover, Cai Weian, assistant researcher in the Environment Division, explained with a research case: according to research findings from the University of Hawaii, using white clover between dwarf pumpkin rows can effectively reduce the population numbers of silverleaf whitefly and aphids on pumpkin leaves, and significantly reduce the severity of the disease, even improving yield. The Hualien District Agricultural Research and Extension Station tried applying white clover in 2015, combined with induced disease-resistance materials, and found it reduced the virus incidence rate by 15% to 40%, significantly reducing the adverse effects of viral infection and stabilizing farmers' returns.

Two comparison areas: on the right, pumpkin seedlings in a field with plastic sheeting laid, contracted severe Fusarium wilt. This is because there was no regulation by white clover, so the Fusarium wilt was more severe (image provided by/Hualien District Agricultural Research and Extension Station). Originally regarded as a weed, little did people know it was a treasure; its benefits do not stop there. The Hualien District Agricultural Research and Extension Station's trials also found that after covering with white clover, soil temperature was lower compared with other treatment areas, and water balance and aeration were both better, which can help pumpkin get through the adverse environment of excessively high temperatures in the later growth stage and prevent infection by Fusarium wilt. "However, such a good cover plant was at first just regarded by people as a weed!" Cai Weian pointed out that white clover is native to North America, and before 1950 it was regarded as a weed, and people's attitude toward it was to eliminate it as quickly as possible. Later, environmental science researchers gradually discovered that white clover is quite good for soil, because it grows quickly, can suppress weed growth, and also has nitrogen-fixing effects, which is very beneficial to soil. "As a green manure, white clover, besides containing more than 70% water, also contains many readily decomposable water-soluble substances, as well as cellulose, lignin, etc., and can improve the soil's physical and chemical properties and biological properties. The benefits are many!" And so white clover turned things around from the bottom, gradually becoming a popular green manure plant; and in recent years, because research has found that if used as a cover plant in biological control, it can effectively reduce the harm of disease-vector insect populations to cucurbits, its value has been rising in a straight line. Taiwan's first on-site application had results beyond expectations.

In research on biological control, Taiwan has mostly focused on developing organic control agents, and has almost rarely worked on virus-related research, so the practical application of white clover (Trifolium repens) in reducing the harm of disease-vector insects is still a first.

After the practical application, Huang Xingsheng was quite satisfied with this brand-new method. He said that after white clover is sown, if weeds grow among it they need to be pulled out by hand, and during this period it is a bit more tiring, but once the white clover grows dense, the weeds are outcompeted and there is no need to pull them anymore. "Pulling weeds by hand is a bit tiring, but the results afterward are worth it."

Cai Weian stated that for farmers this method may increase some costs, because plastic sheeting must first be laid, then white clover seed scattered, which means two rounds of work in operation. In addition, the seed cost of white clover must be added, "about 1500 yuan is needed per fen of land." She said, "But this is only the first time, and afterward, as long as the seed remains in the soil, there is no need for so much expense."

Although labor and cost will be a bit higher, Huang Xingsheng thinks it is very worthwhile. Because ever since planting white clover, most of the harvested fruit has been very healthy. "Less loss is equivalent to more income." He described it bluntly, "For farmers, harvest is profit!"