Plant health diagnosis for sugarcane
Case 1 Gaps in the ratoon row - 1
Use Advanced for doses, plans and diagnosis Tap the level next to the microphone. Core gives quick answers and weather checks. Advanced reasons more deeply for spray programs, disease diagnosis and fertilization plans, and can take a minute or two. Auto lets ORTH choose. Every answer in this course used Advanced. For sugarcane Many problems leave gaps in a ratoon. Keep Advanced on and say what you see above and below ground: how long the gaps are, how the stool base looks and what is inside the rhizome. - 2
Describe what you dig up We described gaps of more than half a metre in the row, dry hollowed stool bases and small white legless larvae inside the rhizomes. ORTH named the sugarcane weevil, Sphenophorus levis, as the leading suspect: cream-white legless larvae with a brown head that tunnel through the stool and rhizome and kill the buds. The main alternative is Migdolus fryanus, with larger larvae deeper in the soil around the root crown. White grubs have legs and a C shape, stem borers have legs and attack the stalk, and waterlogging alone would not explain the larvae. - 3
Confirm it before you treat Map each patch and dig up whole stools at its edge, where vigorous stools turn weak, next to healthy ones. Split the rhizomes lengthwise and look for galleries, fibrous frass, dead buds and larvae, pupae or adults, and sieve the soil around them for Migdolus. Photograph the larva from above and from the side, the head next to a scale, the gallery and the whole stool. Keep the samples from each patch apart, some alive with a piece of rhizome, and send them to the mill’s pest laboratory or a sugarcane entomologist. An adult and the gallery pattern confirm it better than a larva alone. - 4
What to do while you wait Do not spray a blanket insecticide as a test. Flag the patches, keep infested stools, soil and straw out of clean areas, and clean the machinery before it leaves a suspect patch. Extra fertilizer will not bring back stools whose buds are dead. ORTH suggested adding the digging and larva collection to the establishment check already planned for 12 November. Once the pest is identified, measure the affected area before you choose between treating hotspots, filling gaps or renovating, because filling gaps before you control the source often fails again. Case 2 Pustules on the leaves - 5
Tell the two rusts apart On other stools we saw small elongated orange to brown pustules, mostly under the leaf, and leaves drying from the tip. ORTH said it is likely a rust, and that colour alone cannot say which. Orange rust, Puccinia kuehnii, has small bright orange pustules in dense clusters. Brown rust, Puccinia melanocephala, has longer, narrower pustules along the veins, cinnamon to dark reddish brown. Old orange rust pustules also turn brown. Pustules on the underside and dry leaf tips fit both. Flat marks with no loose powder point to a leaf spot, nutrition or stress instead. - 6
Confirm the species, then the variety Pick leaves with fresh pustules, check with a hand lens that they break the leaf surface, and rub single pustules on white tissue: orange powder points to orange rust, cinnamon or reddish brown to brown rust. Photograph the whole leaf and both sides in daylight, and send dry leaves in labelled paper envelopes to a sugarcane pathology laboratory for microscopy or PCR. The variety matters, because resistance is specific to each rust: RB867515 being resistant to one does not cover the other. ORTH found no current rating for RB867515, so the variety informs the diagnosis without deciding it. It rated this answer three stars.
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