Where there is Septoria tritici blotch (STB) in a crop …

Question

BlackTom AI · Accepted Answer

In this question, we’re evaluating what is true when Septoria tritici blotch (STB) is present in a crop.
Option 1: 'The grain filling period will be longer, resulting in pinched grain.' This statement misattributes the symptom and timing to grain development changes caused by STB; STB is a foliar disease that affects leaves, not directly causing pinched grain through longer grain filling, so this option is inaccurate.
Option 2: 'Fungicides should be applied when the first symptoms appear.' While fungicides can be part of a management strategy, recommending application precisely at first symptoms is not universally correct; timings, decisions, and resistance concerns mean that fungicide use is often guided by disease forecasting, risk periods, and product labels rather than symptoms alone. This makes the statement overly simplistic and potentially misleading.
Option 3: 'Disease-free seed should have been sown.' Sowing disease-free seed is generally good practice, but with STB, a major inoculum source is the crop residue (stubble) left from a previous infection. The presence of STB in the crop emphasizes the role of previous-season inoculum, not seed-borne inoculum alone, so this option does not address the main inoculum source.
Option 4: 'The stubble from a previously infected crop may have provided the inoculum.' This option correctly identifies the key epidemiological fact: STB often overwinters or over-summers in crop residue, and infected stubble can serve as a primary inoculum source for current crops. This aligns with our understanding of STB dispersal and infection cycles, making it the accurate choice.
In summary, the other options either misstate the disease’s effects, oversimplify management timing, or miss the central inoculum pathway, whereas option 4 correctly highlights stubble as a potential inoculum source for STB.

AGRI20037_2025_SM2 13. Practice Exam 2025

Where there is Septoria tritici blotch (STB) in a crop …

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