Soil pathogen control with 1,3-D followed by metam sodium and 1,3-D with intermittent water seals was inconsistent between the two experiments, which suggests that specific micro- and macro-level differences in environmental and field conditions may contribute to greater treatment variability and risk to growers.When 1,3-D was sealed with HDPE and VIF, broad leaf weed density was reduced to less than 6 weeds per square meter, which was comparable to methyl bromide . These results are similar to a previous nursery study that indicated 1,3-D or 1,3-D plus chloropicrin sealed with HDPE or VIF resulted in weed seed viability and hand-weeding time comparable to methyl bromide . Generally, intermittent water seals after a 1,3-D application resulted in broad leaf weed density similar to the untreated control. Most weeds germinate near the soil surface,microgreen fodder system thus techniques such as intermittent water seals that limit upward fumigant movement into surface soils can adversely affect weed control.
The other surface treatments 1,3-D dual application and 1,3-D followed by metam sodium had intermediate broad leaf weed densities compared to untreated plots and methyl bromide. All fumigation treatments reduced grass weed populations compared to the control plots; however, the greatest reductions were observed in plots treated with methyl bromide, 1,3-D sealed with HDPE or VIF, and 1,3-D followed by metam sodium. It was clear in this study that effective surface treatments can greatly increase weed control with 1,3-D; however, even the best treatments will likely require supplemental weed control to meet grower expectations.Effects of surface seal treatments and 1,3-D soil fumigation on nursery stock vigor and performance in two nursery trials were evaluated in 2007 to 2010 . In the rose nursery trial, all treatments had similar root stock vigor and number of marketable plants except when 1,3-D was followed by metam sodium. During the 2008 growing season, roses grown in plots treated with 1,3-D followed by metam sodium had lower vigor than the other treatments; however, by harvest at the end of the second year, no differences in marketable plants were observed. In the tree nursery trial, tree root stock vigor was reduced in plots treated with 1,3-D followed by metam sodium and1,3-D with intermittent water seals compared with the other fumigation treatments, but root stock caliper at the end of the first growing season did not differ among treatments.
Compared with some other fumigation-dependent industries, perennial fruit and nut nursery stock production systems face a more difficult transition to methyl bromide alternatives . Despite several years of research, the following significant challenges to widespread adoption of alternatives in the perennial crop nursery industry remain: National and international market expectations for nematode-free nursery stock limit nursery stock producers to alternatives with very high nematode efficacy at significant depths in the soil. To meet California nursery certification requirements, producers are required to use approved fumigant treatments or conduct a post production inspection. A failed inspection may result in an essentially nonsalable crop. Most alternative treatment schedules are based on the use of 1,3-D , a fumigant that faces its own serious and evolving regulatory issues in California. No currently available alternative fumigant can be used in California to meet certification requirements in nurseries with fine-textured soil at registered rates. Methyl iodide, the alternative fumigant with performance most similar to methyl bromide, is not currently registered in the United States due to a voluntary withdrawal by the manufacturer. Concerns over control of weeds and fungal and bacterial pathogens in the short and long term may further limit adoption of alternatives with a narrower pest control spectrum.
Containerized nursery stock production systems are being used in some parts of the industry, but the production costs, market acceptance and long-term viability of this system have not been addressed at the required scale.Adoption of methyl bromide alternatives, where they exist, in the perennial crop nursery industry will ultimately be driven by state and federal regulations and economics. Although it’s heavily regulated, 1,3-D is a viable alternative for growers with coarse-textured soil, but if 1,3-D becomes more difficult to use due to shortages or increasingly stringent regulations, it may be only a short-term solution. No viable fumigant alternatives exist for California nurseries with fine-textured soil, and some of them may be unable to produce certified nursery stock in the absence of methyl bromide. The cost of producing perennial nursery stock using more expensive, laborious or economically risky production methods will ultimately be passed on to customers and could have long-term impacts on the nursery, orchard, vineyard and ornamental industries.Citrus fruit is very important to the Indonesian farmer, since it can give him more income than other crops. According to some surveys , he can get at least five to six times as much income from a 5-6- year-old citrus planting as from groundnut and four to five times as much as from rice cultivated on equal acreages. Because of good yields and prices for certain mandarin varieties, more and more acreage is being planted. Although no exact statistics are available, it is estimated that in West Java alone, at least 10,000 ha are planted with citrus . Except in some places, i.e., the southern part of West Java and the northern part of West Borneo, mandarin trees are not planted as special citrus orchards, but are usually mixed together with other crops. Citrus plantings are scattered throughout the larger islands of Sumatra, Java, Madura, Borneo, Sulawesi, Bali, Lombok, etc. There are varieties that can be grown well at lower altitudes, like the Siam, but there are also good varieties that can grow and give good quality fruit at altitudes of 700 to 900 m like the well-known Garut variety. Therefore,barley fodder system the farmer has the opportunity to choose varieties suited for his situation. The gradual, but steady extension of citrus plantings carries with it some problems that are becoming more and more serious. Nearly every citrus grower knows that in Some places the original good quality mandarin trees which were many years old declined and were replaced by small, chlorotic citrus trees with marble-sized fruits. The farmer could not realize that introductions of new stock material from certain other areas could endanger the already established citrus trees, and instead, soil and climatic factors were blamed for the disease situation. The farmers tried to eliminate the symptoms by putting on more manure and fertilizers, and even by spraying the trees with pesticides. Presently, most of the citrus growers know that these efforts are useless. The magnitude of destruction is not small. In West Java alone, it was estimated that from 1960 onward, not less than 3 million trees were destroyed , and we know that this destruction is still taking place. Research on this problem was begun in 1954 and research workers of the Horticultural Research Institute, the Bogor Institute of Agriculture, and the Padjadjaran University have made contributions. Since deficiency symptoms of some macro- and microelements were found on leaves of declining trees nearly everywhere, much was done to correct these symptoms by applying fertilizers containing these elements to the soil or by foliar sprays. Reitsma et al.were optimistic that some carbamates such as Zn-dithiocarbamate, Fe-dithiocarbamate, and Mn-dithiocarbamate could remedy these respective deficiencies.
Soil applications of NPK fertilization trials together with microelements were made by some other workers at the Bogor Institute of Agriculture. Some of these trials yielded a more-or-less positive result, but generally it was temporary. After the applications had ceased for some months, the deficiency symptoms reappeared as before. The idea that there was not only a shortage of some elements, but that there could be other factors causing the deficiency symptoms was suggested by some workers. Reitsma and Hadiwidjaja stated, “Though as a rule poor drainage and hardpan are the main fac- tors which lower the vitality of the trees, giving rise to injury of the rootlets by secondary parasites, malnutrition, on the other hand, resulting from insufficient or inadequate fertilization may indirectly intensify the severity of the disease.” Indeed. this statement was not totally incorrect, i.e., for trees not affected by the disease which will be discussed later. Tylenchulus semipenetrans. Cobb, a citrus nematode that causes some problems in other citrus regions of the world, was found by Thrower on citrus roots in several places in Java. Also he found Xiphinema sp. He applied Nemagon to correct the general vigor of the trees, but no positive reAsults were obtained. Inoculation trials with T. semipenetrans also failed to produce chlorotic symptoms on the inoculated seedlings, although the nematode was established on the roots . It was Terra who first expressed the opinion that the probable cause of the bad vigor of citrus trees in general, and the decline of some varieties on sour orange, in particular, was tristeza virus. Inoculation trials done by Thrower on lime seedlings indeed proved that tristeza virus was present in the declining mandarin trees tested. For the moment, it seemed certain that tristeza was to blame for the destruction of so many trees. However, if one considers the problem more closely, symptoms manifested on indicator plants such as vein clearing, vein flecking, and stem pitting merely indicate the presence of tristeza, and these symptoms are by no means generally found on declining mandarin or other citrus trees, except perhaps on limes. So these results did not yet prove that the decline was caused bv tristeza. Proof that the decline was caused by a virus or a complex of viruses required that certain symptoms generally present on declining trees could be reproduced constantly on inoculated seedlings of the same variety. Tirtawidjaja showed that certain symptoms could be reproduced consistently on graft-inoculated seedlings of several species and varieties, including the variety of mandarin declining in the field. At that time, there was no knowledge about mycoplasmas causing plant disease, so it was concluded that the cause of the constant and persistent symptoms was a virus or a complex of viruses . Owing to the absence of similarities with symptoms and other properties of known virus diseases at that time, the authors concluded that this was a new virus disease. It was named “Citrus vein phloem degeneration disease,” for the most specific symptom, the collapse of certain cells of the phloem in leaf veins. The phloem of the mature, yellow or chlorotic leaves is much thicker than normal . Sieve tubes and companion cells are collapsed, and form white bands extending from the sclerenchyma to the xylem. Ray cells remain intact, but are filled with abnormal quantities of starch granules.The external and the internal symptoms were used for diagnosis of CVPD,first in Java and later in other islands of western and central Indonesia. In 1964, the disease was found widespread in several places in west Java and was also found in central and southern parts of central Java and in certain areas of east Java . Further surveys in recent years revealed that CVPD is not confined to the island of Java, but is also present in several places in Sumatra. Nearly all provinces of the island have citrus areas with declining trees which show the characteristic symptoms. On the other hand, no indication of the disease was encountered in the citrus areas of west Borneo, south Borneo, Sulawesi , Madura, Lombok, and others, except on limited numbers of trees in some yards of Pontianak and Ujungpandang . So it is Sumatra and Java that suffer the most from CVPD. This is probably due to the fact that Pasarminggu was and still is functioning as a center of distribution for citrus nursery stock, and Pasarminggu is blamed for the distribution of CVPD in Java and Sumatra. A certain mandarin variety was once known only in Pasarminggu, but now it is widely grown throughout Java and Sumatra. The spread of CVPD was further enhanced by the acquired ability of nurserymen to produce budlings. In certain places, which are CVPDendemic areas, hundreds of thousands of mandarin budlings are being produced, sold and distributed to new and old citrus centers. The Garut area is the most important source of CVPD-affected nursery stock. With past experience that one could obtain more income from citrus than from other crops, but without the new knowledge that CVPD can wipe out whole areas of citrus, this nursery material is being used extensively, especially in Java and Sumatra.