The dynamics of rust in guax plants and the situation in Mato Grosso

Last week we concluded another round of surveying the occurrence of soybean guax plants in the main producing regions of Mato Grosso. We were in Campo Verde, Primavera do Leste, Rondonópolis, Alto Garças and the entire Serra da Petrovina, Alto Araguaia, Alto Taquari, Nova Mutum, Lucas do Rio Verde, Sorriso, Sinop, Diamantino, Deciolandia, Campo Novo do Parecis, Sapezal and Campos of Julius.

We also passed through other municipalities, but these were the main ones, the ones we found the most raucous. The highlight for the clean city, well-kept avenues and streets goes again to Lucas do Rio Verde. Primavera do Leste has also improved a lot! On the other hand, there are cities where guaxa soybeans, let's just talk about them and leave the bush aside, appear to have been sown.  

We have to emphasize that guax plants were found in cities and on roadsides, not in crops. The rural producer is doing his job, taking care of his crops. It is up to city halls and companies responsible for the highways to clean them up so as not to harm the next harvest in the State.

It is important to understand the dynamics of rust on guax plants. With the first harvests, at the end of December and beginning of January, grains begin to fall on the roads and cities. This is where the problem sets in every year. This is a cycle that remains active practically throughout the year.

While there is rain, the rust that is on the crops spreads to the guaxes and, without any control, remains active and spreading to neighboring plants and, from there, to the crops. Crop rust also spreads to raccoons in a permanent cycle of inoculum "exchange". 

Late plantings, especially those that have occurred at the end of December, tend to worsen this situation, as it is an even more virulent inoculum, one that "escaped" from several applications during the harvest and also in these late plantings. Raccoons tend to host this more virulent fungus that will spread to the following harvest. 

With the beginning of the drought, in April and May, the rust stabilizes its cycle, but remains active on the leaves of the basswood and on the dry leaves that have fallen to the ground. Some plants, due to water deficiency, deepen their root system, become semi-evergreen and maintain rust in the soil for much longer. It is this rust that we find at this stage of the year.

Any humidity is enough for these plants to resprout and stay alive throughout the entire off-season. The same happens with the younger plants that are born side by side. The youngest ones, as a rule, do not have rust, but they remain alive close to older plants that have the inoculum on the lower leaves. Sometimes, this "granddaughter" raccoon is the daughter of this other, older raccoon. When the rains stabilize and planting begins, this rust rises to the upper leaves of the guaxas, passes to the younger neighboring leaves and from there spreads to the crops. For this reason, I have no doubt that the inoculum that arrives in the region is local, it is active during the sanitary void very close to the crops that will be sown. 

Sorriso, Sapezal, Sinop, Campo Novo do Parecis, Campo Verde and Alto Araguaia were the places with the most voluntary soy plants on the streets and avenues.  

The most serious cases, however, due to the presence of guaxes with sporulating rust, were found in Campos Novo do Parecis, Sinop, Sapezal, Campo Verde, Alto Araguaia and Campos de Júlio (with fewer guaxes). 

Samples were collected to analyze the I86F mutation and sensitivity to Prothioconazole and we will soon publish the results. Stay tuned, because in the last off-season sampling similar to this one carried out in the sanitary void reflected exactly what happened in the 17/18 harvest.

Aprosoja MT, through president Antonio Galvan, has informed the Rural Unions of this and suggested joint action with City Halls to eradicate these plants. We have sent the geographic coordinates of where the guaxes are and WARNING that this is just a sampling, that there are many more guaxes in the municipality, especially in urban areas and along highways. We have already eradicated a lot of things right away, but much more effort is needed for the size of the problem.